Skin pathology Flashcards
What are the two layers of the skin?
- epidermis - stratified squamous epithelium
- dermis - connective tissue layer, provides strength + elasticity, also contains adnexal structures, blood vessles + lymphatics
What structure separates the epidermis and dermis?
basement membrane
Where are melanocytes found?
- scattered along basal layer of epidermis
- just above the basement membrane
Malignant melanoma is a malignant tumour arising from melanocytes. Where do most cases occur?
- most in the skin
- rare cases at other sites eg. oral cavity, eye
How common is melanoma?
- 5th most common cancer in UK
- incidence of melanoma in UK rising faster than any other common cancer
- 2nd most common cancer in adults aged 25-49
What are important risk factors for developing melanoma?
- fair skin (fair or red hair; lots of freckles)
- sun exposure (UV-A and UV-B): amount of sun expsoure, episodes of sun burn
- use of sunbeds
What is acral melanoma?
- type of melanoma that occurs in the palms, soles + under nails (subungual)
- the most common form of melanoma in Asian + Black ethnic groups
- does not appear to be linked to sun exposure
Clinically, most melanomas are identified as pigmented lesions on the skin. The ‘ABCD’ guidelines are useful in distinguishing a melanoma from a benign mole.
What are the ABCD guidelines?
- the ‘ugly duckling’ sign is also useful - a skin lesion that looks different to others that are present
What is a cutaneous malignant melanoma?
- malignant tumour arising from melanocytes in epidermis
- cutaneous (skin)
What are important prognostic factors for malignant melanomas?
-
Breslow thickness - thickness of tumour in mm - v important + forms part of TNM staging:
- melanomas <0.75mm -> 98% 5yr survival
- melanomas >1.5mm -> 40-60% 5yr survival
- melanomas are staged using TNM system
- melanomas are not graded (they are all high grade)
What is meant by ‘melanoma in situ’?
- most melanomas arise de novo (ie not from pre-existing moles (=benign nevi))
- remember that melanocytes normally reside in the basal layer of the epidermis, just above the basement membrane
- melanoma in situ is a lesion in which the abnormal melanocytes are spreading along basal layer of epidermis
- but have not yet invaded through basement membrane
- represents a form of precancer
What do the terms radial growth phase and vertical growth phase refer to?
- radial growth phase = melanoma in situ
- vertical growth phase = malignant melanoma
the terms are not interchangeable but they are roughly equivalent for our purposes
How common is basal cell carcinoma?
- most common type of skin cancer
- accounts for appeox 70% of cases
The majority of basal cell carcinomas (~80%) arise on the head + face.
What are the risk factors for developing BCC?
- same as melanoma
- fair skin
- cumulative UV radiation exposure
How do basal cell carcinomas manifest clinically?
- pearly nodule
- +/- central umbilication or ulceration
What is the microscopic appearance of basal cell carcinomas?
composed of cells which resemble normal basal cells of the epidermis
How are BCCs graded and staged?
- not graded as they are generally low grade ie. indolent behaviour
- staged using TNM system
In regards to the clinical behaviour of BCC, what might happen if left untreated?
- BCCs may show extensive local spread
- hence the old term ‘rodent ulcer’
- however, distant metastasis is v v rare
What is the other type of non-melanoma skin cancer, apart from BCC?
squamous cell carcinoma
What are major risk factors for developing squamous cell carcinoma?
- fair skin + cumulative UV radiation exposure
- immunosuppression (there is a high incidence of cutaneous SCC post-renal transplant)
- chronic skin ulcers (Marjolin ulcers)
Most SCCs occur in areas of direct skin exposure, with a liking for the head + neck
What is the clinical appearance/nature of SCCs?
- typically irregular
- keratotic tumours
- ulcerate + crust
- tend to grow faster than basal cell carcinomas
What is the microscopic appearance of squamous cell carcinomas?
- squamous cell carcinomas composed of tumour cells resemble the squamous cells (keratinocytes) in epidermis
How are squamous cell carcinomas graded and staged?
- well, moderately or poorly differentiated
- staged using TNM system
- risk of lymph node metastases is higher than for BCCs but still only 1-2%
What is acitinic keratosis (=solar keratosis)?
- small brown, dry scaly lesions in sun-exposed sites
- common in the elderly
- risk factors for developing acitinic keratoses are fair skin + sun exposure
- can be difficult to distinguish acitinic keratosis from squamous cell carcinoma + lesions that are tender
- ulcerated or rapidly growing should be biopsied for a definitive diagnosis
What is the microscopic nature of acitinic keratosis?
- cells in epidermis show dysplasia
- but no invasion through basement membrane
- ie. acitinic keratosis is a form of PRE-cancer
- remember only a small % of AKs develop into invasive SCCs
