Skin pathology

Question 1

What are the two layers of the skin?

Answer 1

• epidermis - stratified squamous epithelium
• dermis - connective tissue layer, provides strength + elasticity, also contains adnexal structures, blood vessles + lymphatics

Question 2

What structure separates the epidermis and dermis?

Answer 2

basement membrane

Question 3

Where are melanocytes found?

Answer 3

• scattered along basal layer of epidermis
• just above the basement membrane

Question 4

Malignant melanoma is a malignant tumour arising from melanocytes. Where do most cases occur?

Answer 4

• most in the skin
• rare cases at other sites eg. oral cavity, eye

Question 5

How common is melanoma?

Answer 5

• 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

Question 6

What are important risk factors for developing melanoma?

Answer 6

• 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

Question 7

What is acral melanoma?

Answer 7

• 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

Question 8

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?

Answer 8

• the ‘ugly duckling’ sign is also useful - a skin lesion that looks different to others that are present

Question 9

What is a cutaneous malignant melanoma?

Answer 9

• malignant tumour arising from melanocytes in epidermis
• cutaneous (skin)

Question 10

What are important prognostic factors for malignant melanomas?

Answer 10

• 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)

Question 11

What is meant by ‘melanoma in situ’?

Answer 11

• 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

Question 12

What do the terms radial growth phase and vertical growth phase refer to?

Answer 12

• radial growth phase = melanoma in situ
• vertical growth phase = malignant melanoma

the terms are not interchangeable but they are roughly equivalent for our purposes

Question 13

How common is basal cell carcinoma?

Answer 13

• most common type of skin cancer
• accounts for appeox 70% of cases

Question 14

The majority of basal cell carcinomas (_~80%) arise on the head + face.

What are the risk factors for developing BCC?

Answer 14

• same as melanoma
• fair skin
• cumulative UV radiation exposure

Question 15

How do basal cell carcinomas manifest clinically?

Answer 15

• pearly nodule
• +/- central umbilication or ulceration

Question 16

What is the microscopic appearance of basal cell carcinomas?

Answer 16

composed of cells which resemble normal basal cells of the epidermis

Question 17

How are BCCs graded and staged?

Answer 17

• not graded as they are generally low grade ie. indolent behaviour
• staged using TNM system

Question 18

In regards to the clinical behaviour of BCC, what might happen if left untreated?

Answer 18

• BCCs may show extensive local spread
• hence the old term ‘rodent ulcer’
• however, distant metastasis is v v rare

Question 19

What is the other type of non-melanoma skin cancer, apart from BCC?

Answer 19

squamous cell carcinoma

Question 20

What are major risk factors for developing squamous cell carcinoma?

Answer 20

• 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

Question 21

What is the clinical appearance/nature of SCCs?

Answer 21

• typically irregular
• keratotic tumours
• ulcerate + crust
• tend to grow faster than basal cell carcinomas

Question 22

What is the microscopic appearance of squamous cell carcinomas?

Answer 22

• squamous cell carcinomas composed of tumour cells resemble the squamous cells (keratinocytes) in epidermis

Question 23

How are squamous cell carcinomas graded and staged?

Answer 23

• well, moderately or poorly differentiated
• staged using TNM system
• risk of lymph node metastases is higher than for BCCs but still only 1-2%

Question 24

What is acitinic keratosis (=solar keratosis)?

Answer 24

• 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

Question 25

What is the microscopic nature of acitinic keratosis?

Answer 25

• 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