Editing Non-melanoma skin cancer (section)

== '''Merkel cell carcinoma''' ==

** Risk factors
*** Older age - median 75yo
*** Light skin
*** '''Immunosuppression'''
*** '''Merkel cell polyomavirus infection'''
*** '''UV exposure'''
*** Genetic syndromes
** Pathophysiology
*** Controversial cell of origination
**** Originally thought to be Merkel cells - found in basal layer of epidermis
**** Possibly from immature multipotent stem cell which acquires neuroendocrine features
**** Might not have a single cell of origin
*** May be associated with Merkel cell polyomavirus
**** Found in 80% of MCC
**** May be part of normal flora
*** Aggressive
** Clinically
*** Red-pink to violaceous, firm, solitary, rapidly growing nodule
*** Typically head and neck, but can occur on extremities and buttocks
*** A symptomatic
*** E xpanding rapidly
*** I mmunosuppression
*** O lder that 50yo
*** U V exposed area
***
** Workup
*** Should have imaging of regional nodes
*** CT-PET (FDG) +/- MRIB
** Staging

'''Merkel cell carcinoma TNM pathologic staging AJCC UICC 8th edition'''
{| class="wikitable"
|'''Primary tumor (T)'''
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|'''T category'''
|'''T criteria'''
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|TX
|Primary tumor cannot be assessed (eg, curetted)
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|T0
|No evidence of primary tumor
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|Tis
|''In situ'' primary tumor
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|T1
|Maximum clinical tumor diameter ≤2 cm
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|T2
|Maximum clinical tumor diameter >2 but ≤5 cm
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|T3
|Maximum clinical tumor diameter >5 cm
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|T4
|Primary tumor invades fascia, muscle, cartilage, or bone
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|'''Regional lymph nodes (N)'''
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|'''Pathological (pN)'''
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|'''pN category'''
|'''pN criteria'''
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|pNX
|Regional lymph nodes cannot be assessed (eg, previously removed for another reason or '''not''' removed for pathological evaluation)
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|pN0
|No regional lymph node metastasis detected on pathological evaluation
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|pN1
|Metastasis in regional lymph node(s)
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|pN1a(sn)
|Clinically occult regional lymph node metastasis identified only by sentinel lymph node biopsy
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|pN1a
|Clinically occult regional lymph node metastasis following lymph node dissection
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|pN1b
|Clinically and/or radiologically detected regional lymph node metastasis, microscopically confirmed
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|pN2
|In-transit metastasis (discontinuous from primary tumor; located between primary tumor and draining regional nodal basin, or distal to the primary tumor) '''without''' lymph node metastasis
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|pN3
|In-transit metastasis (discontinuous from primary tumor; located between primary tumor and draining regional nodal basin, or distal to the primary tumor) '''with''' lymph node metastasis
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|'''Distant metastasis (M)'''
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|'''Pathological (M)'''
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|'''M category'''
|'''M criteria'''
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|M0
|No distant metastasis detected on clinical and/or radiologic examination
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|pM1
|Distant metastasis microscopically confirmed
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|pM1a
|Metastasis to distant skin, distant subcutaneous tissue, or distant lymph node(s), microscopically confirmed
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|pM1b
|Metastasis to lung, microscopically confirmed
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|pM1c
|Metastasis to all other distant sites, microscopically confirmed
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|'''Prognostic stage groups'''
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|'''Pathological stage group (pTNM)'''
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|'''When T is...'''
|'''And N is...'''
|'''And M is...'''
|'''Then the stage group is...'''
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|Tis
|N0
|M0
|0
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|T1
|N0
|M0
|I
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|T2-3
|N0
|M0
|IIA
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|T4
|N0
|M0
|IIB
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|T1-4
|N1a(sn) or N1a
|M0
|IIIA
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|T0
|N1b
|M0
|IIIA
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|T1-4
|N1b-3
|M0
|IIIB
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|T0-4
|Any N
|M1
|IV
|}

** Treatment
*** cN0: excision with 1-2cm margins and SLNB
**** Negative SLNB: still consider RTX to nodes if high-risk features are present
**** Positive SLNB: either clearance or RTX
*** cN1: Excision with 1cm margins and radical lymphadenectomy
*** M1: Immunotherapy (avelumab or pembrolizumab). Radiotherapy is often useful to primary tumour.
*** Radiotherapy:
**** Consider in those with <1cm margins, LVI, head and neck primaries, immunocompromise, large primary tumour (>1cm)
**** Consider to nodal bed with high-risk features but negative SLNB
** Prognosis
*** Poor - 70% overall survival at 5 years
*** High local recurrence rates