Malignant Melanoma

 

Epidemiology and Etiology:

    • Highest incidence in Queensland, northern Australia
    • risk factors:
      • sun-sensitive skin type (pale skin, blond or red hair, numerous freckles, tendency to burn and tan poorly)
      • history of painful or blistering sunburns during childhood or adolescence (2 or more episodes before age 15)
      • intermittent intense sun exposure in individuals who are untanned and tan poorly
      • PUVA treatment (15y latency)
      • Tanning salons
      • Presence of certain nevi:
        • large congenital nevi
        • atypical (dysplastic) nevi
        • atypical (dysplastic) nevus syndrome
        • >50 common nevi
        • nevi >6mm diameter
        • lentigo maligna (5% lifetime risk)
      • xeroderma pigmentosum
      • immunosuppression
      • exposure to chemicals (polyvinyl chloride, insecticides, solvents, arsenic ingestion)
    • familial (8-12%)
    • Lentigo maligna melanoma:
      • Elderly
    • Superficial spreading melanoma:
      • Any age
    • Acral lentiginous melanoma:
      • Black people
      • Japanese
      • Taiwanese
      • Elderly predominantly
      • Male preponderance
    • Verrucous melanoma:
      • Middle aged to older males
    • Rare in childhood
    • Other rare reported associations:
      • Cowden’s disease
      • Neurofibromatosis
      • Retinoblastoma
      • Stasis dermatitis
      • Turner’s syndrome, soft tissue sarcomas
      • Subsequent carcinoma of the pancreas
      • Lymphoproliferative disorders
      • Systemic mastocytosis
      • Lynch syndrome
      • HPV-16 virus
      • HIV virus

 

Common sites:

    • skin
      • upper back in men
      • legs and upper back in women
    • oral
    • anogenital
    • esophagus
    • meninges
    • eye
    • Lentigo maligna melanoma:
      • Face and sun-exposed upper extremities
    • Superficial spreading melanoma:
      • Trunk in males
      • Legs in females
      • Any site
    • Nodular melanoma:
      • Any site
    • Acral lentiginous melanoma:
      • Palmar, plantar, and subungual
      • Vulva
      • Oral cavity
      • Mucous surfaces (vagina)
    • Desmoplastic melanoma:
      • Head and neck
    • Verrucous melanoma:
      • Back and limbs

 

Gross features:

    • >1.0cm mostly
    • striking variations in pigmentation
      • amelanotic variants occasionally
    • irregular, often “notched” borders
    • ABCD rule (many exceptions):
      • Assymetry
      • Border irregularity
      • Color variegation
      • Diameter >6mm
    • Lentigo maligna melanoma:
      • Precursor lesion is lentigo maligna (Hutchinson’s melanotic freckle):
        1. irregularly pigmented macule which expands slowly
        2. great variation in colour (tan-brown, black, pink)
      • invasion (vertical growth phase) characterized by thickening
        1. elevated plaques or nodules
    • Superficial spreading melanoma:
      • Shorter radial growth phase than lentigo maligna melanoma
      • Usually at least superficially invasive at the time of presentation
      • Variegated colour
      • Irregular expanding margin
    • Nodular melanoma:
      • Nodular, polypoid
      • Occasionally pedunculated
      • Dark brown or blue-black
    • Acral lentiginous melanoma:
      • Pigmented plaques or nodules
      • Often ulcerated
      • Longitudinal melanonychia (subungual)
    • Desmoplastic melanoma:
      • Spreading indurated plaque
      • Bulky, firm tumefaction
      • Often non-pigmented
      • Areas of lentigo maligna may be overlying or at the periphery
    • Verrucous melanoma:
      • Mistaken for seborrheic keratosis often

 

Histologic features:

    • WHO classification:
      • Superficial spreading melanoma
      • Nodular melanoma
      • Lentigo maligna melanoma
      • Acral lentiginous melanoma
      • Mucosal-lentiginous melanoma
      • Desmoplastic/neurotropic melanoma
      • Melanoma arising from blue nevus
      • Melanoma arising from a giant congenital nevus
      • Melanoma of childhood
      • Nevoid melanoma
      • Persistent melanoma
      • Melanoma, not otherwise classified
    • lack of maturation
    • poorly-formed nests at the junction
    • Pagetoid spread:
      • individual cells at all levels of the epidermis
    • expansile, balloon-like nodules in the dermis
    • cells larger than nevus cells
      • large nuclei with irregular contours
      • chromatin clumped at the periphery
      • prominent eosinophilic nucleolus
    • radial growth phase:
      • intraepidermal proliferation of atypical melanocytes
      • papillary dermis may be involved (‘invasive radial growth phase’)
      • no dermal mitoses allowed
      • radial growth phase should only be reported when present in the absence of a vertical growth phase
    • vertical growth phase:
      • presence of a dominant nest within the papillary dermis
        • larger than any nest within the epidermis or the surrounding dermis
        • should have 25-50 cells
        • composite cells are cytologically distinct from those of the intraepidermal component: shape, size, nuclear or cytoplasmic features, or presence/absence of pigment
      • fully evolved vertical growth phase defined by a dominant nest extending to the papillary-reticular dermal interface or into the reticulare dermis and / or subcutaneous fat (Clark levels III, IV, and V) comprising cells with a  distinct cytomorphology from the intraepidermal radial growth phase component, often with mitoses
    • associated nevus (dysplastic or common) in 35%
    • prognostic factors (in order of importance):
      • Breslow thickness (may simply be a surrogate of tumour volume):
        • From the top of the granular layer to the deepest tumour cell
        • If the lesion is ulcerated, measure from the base of the ulcer
        • <0.76mm is ‘thin’ with excellent prognosis
      • Ulceration (more important than thickness for melanomas > 1.0 mm thickness)
        • Microscopically confirmed
        • Full-thickneess epidermal defect (including absence of basement membrane)
        • Evidence of reactive changes (fibrin deposition, neutrophils)
        • Thinning, effacement, or reactive hyperplasia of the surrounding epidermis
        • Absence of trauma or a recent surgical procedure
        • Typically ulcerated melanomas show invasion through epidermis
      • Sentinel lymph node involvement
      • Mitotic rate / mitotic index (upstage from pT1a to pT1b)
        • 1 or more mitosis per square mm (a single mitosis is enough)
          • >6 per square mm
        • Start at a “hotspot” or a mitosis, and expand from that area until 1 mm squared has been reached (4 HPF in most microscopes)
        • Can say “at least” if there isn’t enough for 1 mm squared
        • Can say “< 1/mm squared” after numerous fields are examined rather than 0 if you prefer
        • Suggest no more than 2 slides with multiple sections be evaluated so that exhaustive evaluation of the lesion is not performed
          • Should be processed in the same manner as other specimens in the lab, not processed in a special manner to increase detection of mitoses
        • Mitoses must be melanocytic and dermal
      • Increased nuclear volume and deviation from diploidy (worse prognosis)
      • Satellite deposits
        • Microsatellitosis defined as presence of tumour nests > 0.05 mm in diameter, in the reticular dermis, panniculus, or vessels beneath the principal invasive tumour but separated from it by at least 0.3 mm of normal tissue on the section in which the Breslow measurement was taken
      • Hemangiolymphatic invasion
      • Lymph node involvement:
        • Regional lymph nodal metastatsis refers to disease confined to 1 draining nodal basin or 2 contiguous draining nodal basins (ex. femoral/iliac, axillary/supraclavicular, cervical/supraclavicular, axillary/femoral, or bilateral axillary or femoral metastases.
        • Mets to nondraining nodal basins is considered M1
        • 7th ed. Defines nodal involvement by presence of any tumour cells regardless of the quantity, size, or mode of detection
      • Perineural invasion
      • Regression (more important for thin / T1 melanomas):
        • Replacement of tumour cells by lymphocytic inflammation (definition)
        • Attenuation of the epidermis and nonlaminated dermal fibrosis with inflammatory cells, melanophagocytosis, and telangiectasia
        • Complete regression is adverse prognostic, as is regression involving > 75% of the lesion
        • Active regression:
          • Heavy lymphocytic infiltrate in the dermis
          • Loss or degeneration of tumour cells (apoptosis)
        • Previous (old) regression:
          • Presence of vascular fibrous tissue
          • With or without melanophages
          • Variable lymphocytic infiltrate
          • ‘nodular melanosis’ if numerous melanophages
      • lymphocytic infiltration
        • ‘brisk’ response is favourable
        • TIL’s not identified (none)
        • TIL’s nonbrisk: only focally or not along the ntire base of the vertical growth phase
        • TIL’s brisk: diffusely infiltrate the entire base of the vertical growth phase or the netire invasive component
      • Clark’s level (more important for thin melanomas):
        • 1 – confined to epidermis (in situ)
        • 2 – present in but does not fil and expand papillary dermis
        • 3 – fills and expands papillary dermis
        • 4 – reticular dermis
        • 5 – subcutaneous fat
      • site
      • histologic subtype
      • coexisting nevus
    • Margins:
      • State whether the tumour is in situ or invasive
      • “safe minimum” has not been established
    • Lentigo maligna melanoma:
      • Single and nests of atypical epidermal melanocytes, usually confined to the basal layer
        • Flattening or absence of rete ridges
        • Continguous and continuous proliferation
        • Uniform atypia
        • Little pagetoid spread
        • ‘Starburst giant cell’ often in basal layer:
          • multinucleate melanocytes with prominent dendritic processes
      • invasive component:
        • spindle cell or epithelioid
      • Epidermal atrophy often
      • Moderate to severe solar elastosis in upper dermis usually
        • Melanophages
        • Small collections of lymphocytes
      • S100 or HMB-45 may highlight microinvasion
      • Areas of regression not uncommon
    • Superficial spreading melanoma:
      • Atypical melanocytes, singly and in nests, at all levels within the epidermis (buckshot scatter)
      • Invasive component:
        • Solid masses or fascicular arrangement
      • May see:
        • Superficial adnexal epithelial involvement
        • Areas of regression
    • Nodular melanoma:
      • no radial growth phase
        • usually epidermal ‘invasion’ by malignant cells directly overlying the dermal mass
      • oval to round epithelioid cells usually
      • mast cells often (as in other types)
    • Acral lentiginous melanoma:
      • Radial growth phase in a lentiginous pattern of atypical melanocytes, with some nesting
        • May look misleadingly benign
      • May be some ‘buckshot scatter’
      • Melanocytes may be plump with surrounding clear halo (lacunar appearance)
        • May have heavily pigmented dendritic processes
      • Hyperplastic epidermis usually
      • May see:
        • Desmoplastic stromal response
        • Osteosarcomatous change in the stroma
    • Verrucous melanoma:
      • Marked epidermal hyperplasia
      • overlying hyperkeratosis
      • Elongation of rete ridges
      • Usually superficial spreading type histologically
    • Desmoplastic / spindle-cell melanomas:
      • Strands of elongated spindle cells surrounded by mature collagen bundles
        • resemble fibroblasts
        • scattered hyperchromatic and even bizarre nuclei
        • nearly always amelanotic
      • Cellularity varies
      • Deeply infiltrative
        • S100 demonstrates better than H&E
      • Lentigo maligna epidermal component often overlying or towards one edge
      • Multinucleate cells often
      • May see:
        • Small foci of neural transformation
        • Neurotropism
        • Scattered collections of lymphocytes and plasma cells
        • Heterotopic bone or cartilage
        • Sweat duct proliferation
    • Minimal deviation melanoma:
      • Histologic features not well defined.
      • Vertical growth phase composed of uniform population of nevoid cells
        • Epithelioid or spindle features may be present
      • Cytologically deviate only minimally from normal nevus cells
    • Nevoid melanoma:
      • Dermal component resembling a benign intradermal nevus
        • Often sheets or cords in part with loss of orderly arrangement of nests
      • intraepidermal component not prominent, and not characteristic of other melanoma type
      • Maturation may be present but impaired
      • Dermal mitoses present
      • Prominent nucleoli in cells in the base
      • subtle cellular pleomorphism often
    • Other variants:
      • Myxoid
      • Balloon cell
      • Signet-ring
      • Rhabdoid
      • Osteogenic
      • Small cell
      • Small-diameter
      • Ganglioneuroblastic
      • Angiomatoid
      • MPNST-like
      • Animal type (equine)
      • Bullous
      • Melanoma of soft parts (clear cell sarcoma)

 

Immunophenotype:

Marker:

Sensitivity:

Specificity:

Masson-Fontana

Schmorl’s

Modified Warthin-Starry

(melanin)

S100

Virtually all

Not good

HMB-45

92%

Melan-A (MART-1)

NKI / C-3

95%

NSE

Vimentin

Cytokeratin

some

EMA (neg)

PCNA

Proliferating cell nuclear antigen (>40% of cells strongly staining)

Ki-67 (MIB-1)

(desmoplastic / spindle cell melanoma) 

 

 

Vimentin

All

NSE

95%

S100 (sometimes only minority of cells)

95%

BFGF

Basic fibroblast growth factor (nuclear)

most

P75 nerve growth factor receptor

Also stains other tumours of neural crest origin

Laminin

Type IV collagen

often

HMB-45 (focal)

0-20%

NKI / C-3

25%

SMA (patchy)

Nearly half

Melan-A (neg)
    • There are now a large number of publications demonstrating excellent correlation between BRAF V600E (VE1)-mutation specific immunohistochemistry and molecular-based analysis. 4 However, in the absence of established proficiency testing or clear regulatory guidelines, laboratories utilizing this immunohistochemistry assay should perform rigorous validation and have available confirmatory molecular testing. 
    • Partial or complete loss of p16 expression often
    •  

 

Molecular features:

    • BRAF mutations (50%) and copy number gains:
      • V600 (95% of BRAF mutations in melanoma):
        • Activating BRAF mutations are present in approximately 50% of all melanomas. Approximately 90% of these mutations occur at amino acid 600
        • V600E (Val600Glu) (c.1799T>A) (majority)
          • Valine residue substituted by glutamic acid at position 600 (Val600Glu) (BRAF^V600E) (>95% of BRAF mutations in melanoma)
            • Most common is T > A at Codon 600
        • Other mutations have been recorded at codon 600, including BRAF V600K, V600D and V600M. (ESMO BRAF Biomarker Factsheet 2015)
          • V600K (Val600Lys) (c.1798_1799GT>AA)
            • Listed in CAP biomarker protocol 2018
          • V600R (c.1798_1799GT>AG)
            • Listed in CAP biomarker protocol 2018
          • V600D (c.1799_1800TG>AT)
            • Listed in CAP biomarker protocol 2018
          • V600M
      • exon 15 mutations in codons surrounding V600
      • mutations in exon 11
      • Constitutively active kinase
        • Activates MAPK pathway
      • 7q31 gain (common)
        • Copy number gains tend to be of mutated alleles
      • Histology (80% predictive in one study)
        • Increased upward scatter of intraepidermal melanocytes
        • Predominance of nests over single cells
        • Thickening of the involved epidermis
        • Sharper demarcation towards the adjacent uninvolved epidermis
        • Larger, rounder, more heavily pigmented cells
      • Therapy implications:
        • Selective BRAF inhibitors, including verafunib, PLX 4032 (now RO5185426) and GSK2118436 have shown unprecedented clinical activity in patients with metastatic melanoma harboring a BRAF mutation
          • V600E mostly
          • V600K responding to BRAF and MEK inhibitors (small numbers)
          • V600R limited case reports showing objective responses
          • Mutations in exon 15 are mostly weaker activators of MEK/ERK pathway than V600 mutants, and response seem to be less impressive (active area of research)
          • > 80% tumour regression early in course of treatment
          • 60% objective responses
          • clinical evidence of resistance emerges eventually
          • progression-free survival for both selective BRAF inhibitors is approximately 6 to 7 months (compare to 2 months for standard therapy)
          • overall survival (?at 6 mo) was improved in a phase III trial comparing PLX4032 to dacarbazine in treatment-naive BRAF mutant metastatic melanoma patients
      • Molecular Biology:
        • Member of the RAF (rapidly accelerated fibrosarcoma) family of serine / threonine kinases
        • Intermediary component of the MAP-kinase pathway
        • Normally this pathway is stimulated in melanocytes by stem-cell factor (KIT) and fibroblast growth factor (FGF)
      • BRAF therapy-induced changes:
        • tissues taken at relapse show increased ERK activation via phosphorylation; genomic profiling at relapse has demonstrated acquired mutations in MEK1 and NRAS in a subset of cases, though additional biochemical adaptations in signaling have also been noted
    • NRAS mutations (15-30%)
      • Activation of MAPK and PI3-kinase pathways
      • Most common are exon 3 at codons 60 and 61 (80%)
        • Gln61Leu
      • Less common exon 2 at codons 12 and 13 (20%)
      • Mutually exclusive to BRAF V600 mutations generally
    • KIT mutations (< 5%)
      • Mucosal, acral, and chronically sun-damaged skin melanomas (most frequently)
      • Scattered throughout the kinase domain in a pattern similar to GIST
        • Unlike GIST, missense mutations are predominant and deletions and insertion/duplications are rare
        • Exons 13 and 17 are more common than in GIST
      • Exons 11 and 13 most common
        • L576P and K642E (50% of KIT mutations in melanoma) (best response in early studies)
        • Exon 11 small insertions and deletions are rare in melanoma
      • Same activating mutations in KIT that can be found in a large proportion of GISTs
      • Copy number gain
      • Existing drugs can be successful (imatinib and sunitinib)
        • Preliminary results show that single-agent efficacy can be observed
          • But the majority of patients do not achieve objective responses
          • Certain mutations confer sensitivity, at least to certain KIT inhibitors (similar to GIST)
          • Low response rate in patients with KIT amplification without mutation
        • No KIT inhibitors are currently approved for melanoma (July 2015)
      • Histology:
        • Lentiginous growth pattern
        • Poor circumscription towards the uninvolved epidermis
      •  
    • GNAQ mutations
      • Activate MAPK pathway
      • Potential for response to AZD6244 (MEK inhibitor)
      • GNAQ:
        • a heterotrimeric protein that couples transmembrane domain receptors to intracellular signalling pathways such as MAPK
    • CDKN2A mutations and losses
      • UV-signature mutations
      • 9p- (deletion / loss) (60%)
    • TP53 mutations
      • UV-signature mutations
    • PTEN mutations and losses
      • UV-signature mutations
      • Activates PI3-kinase pathway
    • MITF amplifications or mutation
    • CTNNB1 mutations (Beta-catenin)
      • WNT pathway
    • STK11:
      • Mutations in Peutz-Jeghers gene (LKB1 / STK11) have been found
    • Genetic patterns in melanoma:
      • Mutations in MAP-kinase and PI3-kinase pathways are common
        • KIT
        • PI3KCA
        • NRAS
        • BRAF
        • PTEN
      • Activation of MITF transcription by amplification of stimulation of upstream factors
      • Chronically sun damaged (CSD) melanomas:
        • NRAS mutations
        • CCND1 copy number gains (11q13) (up to 50%) (infrequent in non-CSD)
        • KIT mutations and copy number gains (30%) (rare in non-CSD)
        • BRAF mutations (15%)
        • Losses on chromosome 10 (< 10%)
      • Non-CSD melanomas:
        • BRAF mutations and copy number gains (chromosome 7) (70%)
        • Losses on chromosome 10 (40%)
          • PTEN is most commonly lost
        • NRAS mutations
      • Acral
        • Gene amplifications common
        • CCND1 amplifications (11q13) (50%) (not in mucosal melanomas typically)
        • Telomerase amplifications (5p15)
        • KIT mutations
        • BRAF mutations (minority)
        • NRAS mutations (minority)
      • Mucosal
        • Gene amplifications common
        • CDK4 amplification
          • Mutually exclusive with p16 loss
        • KIT mutations
        • BRAF mutations (minority)
        • NRAS mutations (minority)
      • Uveal
        • Chromosome 3 losses
          • Prognostic indicator
        • Strong KIT IHC but lacking mutations
        • GNAQ germline mutations (46%)
      • Malignant blue nevi
        • GNAQ germline mutations (50%)
    • familial:
      • CDKN2A (cyclin-dependent kinase inhibitor 2A) gene mutations (nearly 50% of familial melanomas)
        • Encodes for tumour suppressor protein p16
      • CDK4 gene mutations
    • Chromosomal aberrations (rare in benign nevi aside from Spitz and atypical nodular proliferations arising in congenital nevus)
      • Losses (in decreasing order of frequency):
        • 9p
          • Note that these have been reported in dysplastic nevi by LOH studies
        • 10q
        • 9q
        • 6q
        • 8p
        • 11q
      • Gains:
        • 6p
        • 7
        • 1q
        • 8q
        • 17q
        • 20
        • Note: absence of 11p gain (as seen in Spitz)
    • “…it is likely that over the next few years a molecular classification of melanoma will become dominant and be used in future editions.” (McKee 2012)
      • “…melanoma is not a homogeneous disease entity, but is in fact comprised of distinct classes.”
      • “it is remarkable, however, that the emerging genetic characteristics show considerable correlation with the orginal melanoma types.  However, the overlap is not perfect…”
    • Pathways dysregulated:
      • MAP-kinase
      • PI3-kinase
      • DNA-damaged-induced sensescence
        • p53
    •  

 

Other features:

    • Other prognostic factors:
      • Clinical stage
      • gender
        • female – better prognosis
      • site:
        • extremity – better prognosis
      • vitiligo (favourable)
      • age
        • younger – better prognosis
      • adverse immunohistochemical factors:
        • metallothionein
        • osteonectin
        • integrins
        • serum S100
    • sentinel node examination should be considered for T1b and above
    • no metastatic potential unless vertical growth present
    • risk factors
      • sunlight exposure
      • lighter skin type
      • dysplastic nevus
      • family history
    • clinical:
      • change in color, size, or shape in a pigmented lesion
      • itching or pain (not usually)
      • new pigmented lesion as an adult