Basal Cell Carcinoma (BCC)

Overview

Definition

Basal cell Basal Cell Erythema Multiforme carcinoma is a skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Skin: Structure and Functions cancer arising from the basal layer of epidermis Epidermis The external, nonvascular layer of the skin. It is made up, from within outward, of five layers of epithelium: (1) basal layer (stratum basale epidermidis); (2) spinous layer (stratum spinosum epidermidis); (3) granular layer (stratum granulosum epidermidis); (4) clear layer (stratum lucidum epidermidis); and (5) horny layer (stratum corneum epidermidis). Skin: Structure and Functions and its appendages.

Epidemiology

• Most common cancer worldwide
• Most common skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Skin: Structure and Functions malignancy Malignancy Hemothorax
• Age-adjusted incidence Incidence The number of new cases of a given disease during a given period in a specified population. It also is used for the rate at which new events occur in a defined population. It is differentiated from prevalence, which refers to all cases in the population at a given time. Measures of Disease Frequency in the United States is 226 per 100,000 person-years.
• > 1 million basal cell Basal Cell Erythema Multiforme carcinomas are treated annually in the United States.
• Men > women
• Incidence Incidence The number of new cases of a given disease during a given period in a specified population. It also is used for the rate at which new events occur in a defined population. It is differentiated from prevalence, which refers to all cases in the population at a given time. Measures of Disease Frequency increases with age.

Risk factors

• Ultraviolet (UV) light exposure:
  • Sun exposure (outdoor workers)
  • Tanning beds
  • Phototherapy Phototherapy Treatment of disease by exposure to light, especially by variously concentrated light rays or specific wavelengths. Hyperbilirubinemia of the Newborn for psoriasis Psoriasis Psoriasis is a common T-cell-mediated inflammatory skin condition. The etiology is unknown, but is thought to be due to genetic inheritance and environmental triggers. There are 4 major subtypes, with the most common form being chronic plaque psoriasis. Psoriasis
• Advanced age
• Arsenic Arsenic A shiny gray element with atomic symbol as, atomic number 33, and atomic weight 75. It occurs throughout the universe, mostly in the form of metallic arsenides. Most forms are toxic. According to the fourth annual report on carcinogens, arsenic and certain arsenic compounds have been listed as known carcinogens. Metal Poisoning (Lead, Arsenic, Iron) exposure (e.g., contaminated drinking water, contaminated seafood)
• Ionizing radiation Radiation Emission or propagation of acoustic waves (sound), electromagnetic energy waves (such as light; radio waves; gamma rays; or x-rays), or a stream of subatomic particles (such as electrons; neutrons; protons; or alpha particles). Osteosarcoma
• Chronic immunosuppression 
• Genetics Genetics Genetics is the study of genes and their functions and behaviors. Basic Terms of Genetics: 
  • Fair complexion
  • Personal and family history Family History Adult Health Maintenance of basal cell Basal Cell Erythema Multiforme carcinoma
  • Genetic syndromes:
    • Gorlin syndrome (characterized by developmental anomalies and multiple basal cell Basal Cell Erythema Multiforme carcinomas)
    • Xeroderma pigmentosum Xeroderma pigmentosum A rare, pigmentary, and atrophic autosomal recessive disease. It is manifested as an extreme photosensitivity to ultraviolet rays as the result of a deficiency in the enzyme that permits excisional repair of ultraviolet-damaged DNA. Lentigo Maligna ( mutation Mutation Genetic mutations are errors in DNA that can cause protein misfolding and dysfunction. There are various types of mutations, including chromosomal, point, frameshift, and expansion mutations. Types of Mutations in repair of UV-induced DNA damage DNA Damage Injuries to DNA that introduce deviations from its normal, intact structure and which may, if left unrepaired, result in a mutation or a block of DNA replication. These deviations may be caused by physical or chemical agents and occur by natural or unnatural, introduced circumstances. They include the introduction of illegitimate bases during replication or by deamination or other modification of bases; the loss of a base from the DNA backbone leaving an abasic site; single-strand breaks; double strand breaks; and intrastrand (pyrimidine dimers) or interstrand crosslinking. Damage can often be repaired (DNA repair). If the damage is extensive, it can induce apoptosis. DNA Repair Mechanisms)
    • Bazex–Dupré–Christol syndrome (milia, hypotrichosis, multiple basal cell Basal Cell Erythema Multiforme carcinomas)
    • Oculocutaneous albinism Oculocutaneous albinism Heterogeneous group of autosomal recessive disorders comprising at least four recognized types, all having in common varying degrees of hypopigmentation of the skin, hair, and eyes. The two most common are the tyrosinase-positive and tyrosinase-negative types. Albinism (disorder in melanin Melanin Insoluble polymers of tyrosine derivatives found in and causing darkness in skin (skin pigmentation), hair, and feathers providing protection against sunburn induced by sunlight. Carotenes contribute yellow and red coloration. Seborrheic Keratosis synthesis Synthesis Polymerase Chain Reaction (PCR))

Pathophysiology and Clinical Presentation

Pathogenesis

• UV radiation Radiation Emission or propagation of acoustic waves (sound), electromagnetic energy waves (such as light; radio waves; gamma rays; or x-rays), or a stream of subatomic particles (such as electrons; neutrons; protons; or alpha particles). Osteosarcoma:
  • Most significant factor
  • UVA and UVB light → DNA damage DNA Damage Injuries to DNA that introduce deviations from its normal, intact structure and which may, if left unrepaired, result in a mutation or a block of DNA replication. These deviations may be caused by physical or chemical agents and occur by natural or unnatural, introduced circumstances. They include the introduction of illegitimate bases during replication or by deamination or other modification of bases; the loss of a base from the DNA backbone leaving an abasic site; single-strand breaks; double strand breaks; and intrastrand (pyrimidine dimers) or interstrand crosslinking. Damage can often be repaired (DNA repair). If the damage is extensive, it can induce apoptosis. DNA Repair Mechanisms
  • Genes Genes A category of nucleic acid sequences that function as units of heredity and which code for the basic instructions for the development, reproduction, and maintenance of organisms. DNA Types and Structure most damaged by UV light UV light That portion of the electromagnetic spectrum immediately below the visible range and extending into the x-ray frequencies. The longer wavelengths (near-uv or biotic or vital rays) are necessary for the endogenous synthesis of vitamin D and are also called antirachitic rays; the shorter, ionizing wavelengths (far-uv or abiotic or extravital rays) are viricidal, bactericidal, mutagenic, and carcinogenic and are used as disinfectants. Bullous Pemphigoid and Pemphigus Vulgaris involve the hedgehog signaling pathway.
• Common mutations:
  • Patched homolog 1 (PTCH1) mutations (found in majority of basal cell Basal Cell Erythema Multiforme carcinoma cases):
    • PTCH1 encodes a protein in the hedgehog pathway.
    • In the resting state, patched homolog 1 (PTCH1) protein normally inhibits smoothened homolog (SMO).
    • When the sonic hedgehog protein binds PTCH1 protein → PTCH1 is degraded → SMO is released
    • This process leads to a series of interacting proteins Proteins Linear polypeptides that are synthesized on ribosomes and may be further modified, crosslinked, cleaved, or assembled into complex proteins with several subunits. The specific sequence of amino acids determines the shape the polypeptide will take, during protein folding, and the function of the protein. Energy Homeostasis → GLI transcription factors Transcription Factors Endogenous substances, usually proteins, which are effective in the initiation, stimulation, or termination of the genetic transcription process. Stages of Transcription activated → cell proliferation
    • General effect of PTCH1 gene Gene A category of nucleic acid sequences that function as units of heredity and which code for the basic instructions for the development, reproduction, and maintenance of organisms. Basic Terms of Genetics mutations: unbound SMO allows unregulated cell growth
  • TP53 mutations also seen in 20%–60% of sporadic Sporadic Selective IgA Deficiency basal cell Basal Cell Erythema Multiforme carcinomas:
    • TP53 normally involved in apoptosis Apoptosis A regulated cell death mechanism characterized by distinctive morphologic changes in the nucleus and cytoplasm, including the endonucleolytic cleavage of genomic DNA, at regularly spaced, internucleosomal sites, I.e., DNA fragmentation. It is genetically-programmed and serves as a balance to mitosis in regulating the size of animal tissues and in mediating pathologic processes associated with tumor growth. Ischemic Cell Damage and DNA DNA A deoxyribonucleotide polymer that is the primary genetic material of all cells. Eukaryotic and prokaryotic organisms normally contain DNA in a double-stranded state, yet several important biological processes transiently involve single-stranded regions. DNA, which consists of a polysugar-phosphate backbone possessing projections of purines (adenine and guanine) and pyrimidines (thymine and cytosine), forms a double helix that is held together by hydrogen bonds between these purines and pyrimidines (adenine to thymine and guanine to cytosine). DNA Types and Structure repair
    • Mutations → cell proliferation and defective DNA DNA A deoxyribonucleotide polymer that is the primary genetic material of all cells. Eukaryotic and prokaryotic organisms normally contain DNA in a double-stranded state, yet several important biological processes transiently involve single-stranded regions. DNA, which consists of a polysugar-phosphate backbone possessing projections of purines (adenine and guanine) and pyrimidines (thymine and cytosine), forms a double helix that is held together by hydrogen bonds between these purines and pyrimidines (adenine to thymine and guanine to cytosine). DNA Types and Structure
  • Other genes Genes A category of nucleic acid sequences that function as units of heredity and which code for the basic instructions for the development, reproduction, and maintenance of organisms. DNA Types and Structure: SMO, SUFU

Clinical and histologic features

• Disease characteristics: 
  • Lesion can be a papule Papule Elevated lesion < 1 cm in diameter Generalized and Localized Rashes, patch Patch Nonpalpable lesion > 1 cm in diameter Generalized and Localized Rashes, or plaque Plaque Primary Skin Lesions.
  • Most remain localized but can become aggressive
  • Rarely metastasize (< 0.05%)
  • Slow-growing
• Basal cell Basal Cell Erythema Multiforme carcinoma distribution:
  • Face: 70% ( nose Nose The nose is the human body’s primary organ of smell and functions as part of the upper respiratory system. The nose may be best known for inhaling oxygen and exhaling carbon dioxide, but it also contributes to other important functions, such as tasting. The anatomy of the nose can be divided into the external nose and the nasal cavity. Nose Anatomy (External & Internal), cheeks Cheeks The part of the face that is below the eye and to the side of the nose and mouth. Melasma, forehead Forehead The part of the face above the eyes. Melasma, nasolabial folds, and eyelids Eyelids Each of the upper and lower folds of skin which cover the eye when closed. Blepharitis)
  • Trunk: 15%
  • Remaining body parts: 15%
• Histopathology:
  • Cells of tumor Tumor Inflammation islands with palisading arrangement at the periphery
  • Cellular apoptosis Apoptosis A regulated cell death mechanism characterized by distinctive morphologic changes in the nucleus and cytoplasm, including the endonucleolytic cleavage of genomic DNA, at regularly spaced, internucleosomal sites, I.e., DNA fragmentation. It is genetically-programmed and serves as a balance to mitosis in regulating the size of animal tissues and in mediating pathologic processes associated with tumor growth. Ischemic Cell Damage
  • Scattered mitotic activity in the dermis Dermis A layer of vascularized connective tissue underneath the epidermis. The surface of the dermis contains innervated papillae. Embedded in or beneath the dermis are sweat glands; hair follicles; and sebaceous glands. Skin: Structure and Functions
• Histologic types:
  • Nodular basal cell Basal Cell Erythema Multiforme carcinoma
  • Superficial basal cell Basal Cell Erythema Multiforme carcinoma
  • Morpheaphorm (sclerosing) basal cell Basal Cell Erythema Multiforme carcinoma
  • Other, more rare, types:
    • Basosquamous cell carcinoma
    • Pigmented basal cell Basal Cell Erythema Multiforme carcinoma

Diagnosis and Staging

Diagnosis

History:

• Family history Family History Adult Health Maintenance of genetic diseases
• Personal history of previous skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Skin: Structure and Functions cancers
• History of excessive sun exposure
• HIV-positive status or other forms of immunocompromise

Physical exam:

• Thorough skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Skin: Structure and Functions examination should be performed.
• Assess for palpable lymphadenopathy Lymphadenopathy Lymphadenopathy is lymph node enlargement (> 1 cm) and is benign and self-limited in most patients. Etiologies include malignancy, infection, and autoimmune disorders, as well as iatrogenic causes such as the use of certain medications. Generalized lymphadenopathy often indicates underlying systemic disease. Lymphadenopathy.

Dermoscopy Dermoscopy A noninvasive technique that enables direct microscopic examination of the surface and architecture of the skin. Seborrheic Keratosis:

• Arborizing vessels
• Blue-gray ovoid nests
• Ulceration Ulceration Corneal Abrasions, Erosion, and Ulcers
• Lack of pigmented network (unlike melanocytic lesions)

Biopsy Biopsy Removal and pathologic examination of specimens from the living body. Ewing Sarcoma:

• Establishes definitive diagnosis
• Shave, punch, or excisional technique can be used.

Staging Staging Methods which attempt to express in replicable terms the extent of the neoplasm in the patient. Grading, Staging, and Metastasis

• Basal cell Basal Cell Erythema Multiforme carcinoma metastasis Metastasis The transfer of a neoplasm from one organ or part of the body to another remote from the primary site. Grading, Staging, and Metastasis is rare and is thus not usually staged.
• Often, the cancer is treated before it spreads.
• Sites of metastasis Metastasis The transfer of a neoplasm from one organ or part of the body to another remote from the primary site. Grading, Staging, and Metastasis:
  • Regional lymph nodes Lymph Nodes They are oval or bean shaped bodies (1 – 30 mm in diameter) located along the lymphatic system. Lymphatic Drainage System: Anatomy
  • Lungs Lungs Lungs are the main organs of the respiratory system. Lungs are paired viscera located in the thoracic cavity and are composed of spongy tissue. The primary function of the lungs is to oxygenate blood and eliminate CO2. Lungs: Anatomy
  • Bones
  • Liver Liver The liver is the largest gland in the human body. The liver is found in the superior right quadrant of the abdomen and weighs approximately 1.5 kilograms. Its main functions are detoxification, metabolism, nutrient storage (e.g., iron and vitamins), synthesis of coagulation factors, formation of bile, filtration, and storage of blood. Liver: Anatomy
  • Skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Skin: Structure and Functions
• Imaging: CT or MRI used for evaluation of metastasis Metastasis The transfer of a neoplasm from one organ or part of the body to another remote from the primary site. Grading, Staging, and Metastasis
• Staging Staging Methods which attempt to express in replicable terms the extent of the neoplasm in the patient. Grading, Staging, and Metastasis follows that for cutaneous squamous cell carcinoma Squamous cell carcinoma Cutaneous squamous cell carcinoma (cSCC) is caused by malignant proliferation of atypical keratinocytes. This condition is the 2nd most common skin malignancy and usually affects sun-exposed areas of fair-skinned patients. The cancer presents as a firm, erythematous, keratotic plaque or papule. Squamous Cell Carcinoma (SCC) but is applicable only to head and neck Neck The part of a human or animal body connecting the head to the rest of the body. Peritonsillar Abscess lesions (American Joint Committee on Cancer, 8th edition).
• Stages:
  • Stage 0: cancer involves only the epidermis Epidermis The external, nonvascular layer of the skin. It is made up, from within outward, of five layers of epithelium: (1) basal layer (stratum basale epidermidis); (2) spinous layer (stratum spinosum epidermidis); (3) granular layer (stratum granulosum epidermidis); (4) clear layer (stratum lucidum epidermidis); and (5) horny layer (stratum corneum epidermidis). Skin: Structure and Functions (in situ)
  • Stage I: 
    • Cancer is not large (≤ 2 cm).
    • No spread to the lymph nodes Lymph Nodes They are oval or bean shaped bodies (1 – 30 mm in diameter) located along the lymphatic system. Lymphatic Drainage System: Anatomy or other organs
  • Stage II: 
    • Cancer is large (>2 cm but ≤ 4 cm). 
    • No spread to lymph nodes Lymph Nodes They are oval or bean shaped bodies (1 – 30 mm in diameter) located along the lymphatic system. Lymphatic Drainage System: Anatomy or other organs
  • Stage III: 
    • Cancer > 4 cm or cancer of any size with deep, perineural or minor bone Bone Bone is a compact type of hardened connective tissue composed of bone cells, membranes, an extracellular mineralized matrix, and central bone marrow. The 2 primary types of bone are compact and spongy. Bones: Structure and Types invasion and/or spread to 1 ipsilateral lymph Lymph The interstitial fluid that is in the lymphatic system. Secondary Lymphatic Organs node (no extranodal extension Extension Examination of the Upper Limbs)
    • No spread to other organs
  • Stage IV: lesions of any size; spread to other organs (distant metastasis Metastasis The transfer of a neoplasm from one organ or part of the body to another remote from the primary site. Grading, Staging, and Metastasis)

Management and Prognosis

Treatment approach

Assess risk of recurrence:

• Helps determine treatment of choice
• Inadequate treatment of high-risk lesions can result in recurrence and complications (e.g., deformities).
• High-risk features:
  • Location: face, ears, hands, and feet
  • Size:
    • ≥ 10 mm MM Multiple myeloma (MM) is a malignant condition of plasma cells (activated B lymphocytes) primarily seen in the elderly. Monoclonal proliferation of plasma cells results in cytokine-driven osteoclastic activity and excessive secretion of IgG antibodies. Multiple Myeloma on head, neck Neck The part of a human or animal body connecting the head to the rest of the body. Peritonsillar Abscess, and pretibia
    • ≥ 20 mm MM Multiple myeloma (MM) is a malignant condition of plasma cells (activated B lymphocytes) primarily seen in the elderly. Monoclonal proliferation of plasma cells results in cytokine-driven osteoclastic activity and excessive secretion of IgG antibodies. Multiple Myeloma in other areas
  • Aggressive variants: morpheaform, basosquamous, micronodular
  • Recurrent lesions
  • Perineural invasion
  • Poorly defined borders
  • Basal cell Basal Cell Erythema Multiforme carcinomas in previous radiation Radiation Emission or propagation of acoustic waves (sound), electromagnetic energy waves (such as light; radio waves; gamma rays; or x-rays), or a stream of subatomic particles (such as electrons; neutrons; protons; or alpha particles). Osteosarcoma sites
  • Immunocompromised patient Immunocompromised patient A human or animal whose immunologic mechanism is deficient because of an immunodeficiency disorder or other disease or as the result of the administration of immunosuppressive drugs or radiation. Herpes Zoster (Shingles)

Surgery:

• Standard surgical excision: 
  • 1st-line treatment for low-risk lesions
  • Margins: 4–5 mm MM Multiple myeloma (MM) is a malignant condition of plasma cells (activated B lymphocytes) primarily seen in the elderly. Monoclonal proliferation of plasma cells results in cytokine-driven osteoclastic activity and excessive secretion of IgG antibodies. Multiple Myeloma
• Mohs micrographic surgery:
  • 1st-line treatment for high-risk lesions
  • For facial lesions/cosmetically sensitive areas (less normal tissue resected)

Alternative therapies: 

• Options for patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship who are poor surgical candidates or who prefer not to have surgery:
  • Topical chemotherapy Chemotherapy Osteosarcoma (e.g., imiquimod Imiquimod A topically-applied aminoquinoline immune modulator that induces interferon production. It is used in the treatment of external genital and perianal warts, superficial carcinoma, basal cell; and actinic keratosis. Hypertrophic and Keloid Scars or fluorouracil Fluorouracil A pyrimidine analog that is an antineoplastic antimetabolite. It interferes with DNA synthesis by blocking the thymidylate synthetase conversion of deoxyuridylic acid to thymidylic acid. Bowen Disease and Erythroplasia of Queyrat):
    • Low-risk sites
    • 6-week treatment
    • Skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Skin: Structure and Functions irritation is a side effect.
  • Electrodesiccation Electrodesiccation Seborrheic Keratosis and curettage Curettage A scraping, usually of the interior of a cavity or tract, for removal of new growth or other abnormal tissue, or to obtain material for tissue diagnosis. It is performed with a curet (curette), a spoon-shaped instrument designed for that purpose. Benign Bone Tumors:
    • Can be used for small low-risk basal cell Basal Cell Erythema Multiforme carcinomas
    • Risk of incomplete tumor Tumor Inflammation removal
  • Cryosurgery:
    • Not for high-risk lesions
    • Can result in scarring Scarring Inflammation and hypopigmentation Hypopigmentation A condition caused by a deficiency or a loss of melanin pigmentation in the epidermis, also known as hypomelanosis. Hypopigmentation can be localized or generalized, and may result from genetic defects, trauma, inflammation, or infections. Malassezia Fungi
  • Radiotherapy: for high-risk lesions in poor surgical candidates

Therapy for advanced disease: 

• For metastasis Metastasis The transfer of a neoplasm from one organ or part of the body to another remote from the primary site. Grading, Staging, and Metastasis or locally advanced basal cell Basal Cell Erythema Multiforme carcinoma that is not amenable to radiotherapy or surgery
• Inhibitor of sonic hedgehog pathway: vismodegib, sonidegib

Prognosis Prognosis A prediction of the probable outcome of a disease based on a individual’s condition and the usual course of the disease as seen in similar situations. Non-Hodgkin Lymphomas

• Overall prognosis Prognosis A prediction of the probable outcome of a disease based on a individual’s condition and the usual course of the disease as seen in similar situations. Non-Hodgkin Lymphomas is excellent.
• Metastatic potential: 0.05%–0.1%.
• Population-based case mortality Mortality All deaths reported in a given population. Measures of Health Status: 0.05%.

Differential Diagnosis

• Squamous cell carcinoma Squamous cell carcinoma Cutaneous squamous cell carcinoma (cSCC) is caused by malignant proliferation of atypical keratinocytes. This condition is the 2nd most common skin malignancy and usually affects sun-exposed areas of fair-skinned patients. The cancer presents as a firm, erythematous, keratotic plaque or papule. Squamous Cell Carcinoma (SCC): second most common skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Skin: Structure and Functions cancer: Squamous cell carcinoma Squamous cell carcinoma Cutaneous squamous cell carcinoma (cSCC) is caused by malignant proliferation of atypical keratinocytes. This condition is the 2nd most common skin malignancy and usually affects sun-exposed areas of fair-skinned patients. The cancer presents as a firm, erythematous, keratotic plaque or papule. Squamous Cell Carcinoma (SCC) usually presents as a firm, erythematous, keratotic plaque Plaque Primary Skin Lesions or papule Papule Elevated lesion < 1 cm in diameter Generalized and Localized Rashes. Diagnosis is through biopsy Biopsy Removal and pathologic examination of specimens from the living body. Ewing Sarcoma. Histopathologic examination confirms the diagnosis by showing findings such as atypical keratinocytes Keratinocytes Epidermal cells which synthesize keratin and undergo characteristic changes as they move upward from the basal layers of the epidermis to the cornified (horny) layer of the skin. Successive stages of differentiation of the keratinocytes forming the epidermal layers are basal cell, spinous or prickle cell, and the granular cell. Skin: Structure and Functions infiltrating into the dermis Dermis A layer of vascularized connective tissue underneath the epidermis. The surface of the dermis contains innervated papillae. Embedded in or beneath the dermis are sweat glands; hair follicles; and sebaceous glands. Skin: Structure and Functions.
• Dermatofibroma: a common mesenchymal growth of the skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Skin: Structure and Functions where skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Skin: Structure and Functions fibroblasts Fibroblasts Connective tissue cells which secrete an extracellular matrix rich in collagen and other macromolecules. Sarcoidosis are the major constituents: Dermatofibroma usually presents as a firm, indurated, mobile nodule Nodule Chalazion measuring about 0.5–1 cm. Upon lateral compression Compression Blunt Chest Trauma, a dimple-like depression in the overlying skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Skin: Structure and Functions appears (“buttonhole” sign). 
• Melanoma Melanoma Melanoma is a malignant tumor arising from melanocytes, the melanin-producing cells of the epidermis. These tumors are most common in fair-skinned individuals with a history of excessive sun exposure and sunburns. Melanoma: skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Skin: Structure and Functions malignancy Malignancy Hemothorax arising from melanocytes Melanocytes Mammalian pigment cells that produce melanins, pigments found mainly in the epidermis, but also in the eyes and the hair, by a process called melanogenesis. Coloration can be altered by the number of melanocytes or the amount of pigment produced and stored in the organelles called melanosomes. The large non-mammalian melanin-containing cells are called melanophores. Skin: Structure and Functions: Melanoma Melanoma Melanoma is a malignant tumor arising from melanocytes, the melanin-producing cells of the epidermis. These tumors are most common in fair-skinned individuals with a history of excessive sun exposure and sunburns. Melanoma presents as irregular pigmented lesions and can resemble pigmented variants of basal cell Basal Cell Erythema Multiforme carcinoma. Diagnosis is confirmed by biopsy Biopsy Removal and pathologic examination of specimens from the living body. Ewing Sarcoma. This condition carries a significantly worse prognosis Prognosis A prediction of the probable outcome of a disease based on a individual’s condition and the usual course of the disease as seen in similar situations. Non-Hodgkin Lymphomas than basal cell Basal Cell Erythema Multiforme carcinoma.
• Actinic keratosis Actinic keratosis Actinic keratosis (AK) is a precancerous skin lesion that affects sun-exposed areas. The condition presents as small, non-tender macules/papules with a characteristic sandpaper-like texture that can become erythematous scaly plaques. Actinic Keratosis: benign Benign Fibroadenoma keratinocytic lesion considered a precursor to squamous cell carcinoma Squamous cell carcinoma Cutaneous squamous cell carcinoma (cSCC) is caused by malignant proliferation of atypical keratinocytes. This condition is the 2nd most common skin malignancy and usually affects sun-exposed areas of fair-skinned patients. The cancer presents as a firm, erythematous, keratotic plaque or papule. Squamous Cell Carcinoma (SCC): Lesions of actinic keratosis Actinic keratosis Actinic keratosis (AK) is a precancerous skin lesion that affects sun-exposed areas. The condition presents as small, non-tender macules/papules with a characteristic sandpaper-like texture that can become erythematous scaly plaques. Actinic Keratosis present as scaly erythematous macules. Diagnosis is established by biopsy Biopsy Removal and pathologic examination of specimens from the living body. Ewing Sarcoma.
• Inflammatory skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Skin: Structure and Functions conditions: Psoriasis Psoriasis Psoriasis is a common T-cell-mediated inflammatory skin condition. The etiology is unknown, but is thought to be due to genetic inheritance and environmental triggers. There are 4 major subtypes, with the most common form being chronic plaque psoriasis. Psoriasis and eczema Eczema Atopic dermatitis, also known as eczema, is a chronic, relapsing, pruritic, inflammatory skin disease that occurs more frequently in children, although adults can also be affected. The condition is often associated with elevated serum levels of IgE and a personal or family history of atopy. Skin dryness, erythema, oozing, crusting, and lichenification are present. Atopic Dermatitis (Eczema) can present with erythematous papules and plaques and clinically resemble superficial basal cell Basal Cell Erythema Multiforme carcinoma. Diagnosis is made with a thorough exam, dermoscopy Dermoscopy A noninvasive technique that enables direct microscopic examination of the surface and architecture of the skin. Seborrheic Keratosis, and biopsy Biopsy Removal and pathologic examination of specimens from the living body. Ewing Sarcoma.