Malignant melanoma
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Malignant melanoma, also melanoma, is an aggressive type of skin cancer that can be diagnostically challenging for pathologists.
It fits into the larger category of melanocytic lesions which includes many benign entities, a number of which can be difficult to distinguish from melanoma.
General
- AKA Malignant melanoma.
- Main DDx: melanocytic lesions - especially if pigmented.
- Known as the great mimicker in pathology; it may look like many things.
Clinical
- ABCD = asymmetric, borders (irregular), colour (black), diameter (large).
Microscopic
Features:
- Classic appearance of melanoma:
- Loosely cohesive; mix of small nests of cells, single cells.
- Nests often have clefting with surrounding tissue.
- Mixed of spindle and ovoid cell morphology.
- +/-Occasional large binucleated cells.
- Cytoplasm: brown pigment (melanin).
- Prominent (large) red nucleoli (like in serous carcinoma of the ovary).
- Marked nuclear pleomorphism - variation in cell size, shape & staining (like in serous carcinoma of the ovary).
- Nuclear pseudoinclusions (like in papillary thyroid carcinoma).
- Loosely cohesive; mix of small nests of cells, single cells.
Notes:
- Can look almost like anything.
- Like it is said that sarcoidosis is in every internal medicine DDx... melanoma is every pathologic DDx.
DDx
- Carcinoma.
- Serous carcinoma - both serous carcinoma and melanoma have a large nucleolus.
- Sarcoma - as may have spindle cells.
- Clear cell sarcoma.
- Metaplastic carcinoma.
- Epithelioid angiosarcoma.
- Lymphoma.
- Other melanocytic lesions.
Metastatic vs. primary
Primary lesions should have:
- Epidermal involvement.
Metastatic lesions classically have:
- Tumour angiotropism (tumours cells cluster around vessels).
- Intravascular invasion.
- No epidermal component.
Note:
- Histology is not definitive for metastatic melanoma vs. primary melanoma; epidermal involvement may be seen in mets.
- History/clinical is important for differentiation.
Breslow thickness
- Depth measured from stratum granulosum to deepest intradermal tumour cell - predictive of survival.[1]
Subtypes
| Subtype name | Key feature | Microscopic additional | DDx | Image | Notes/other |
| Melanoma in situ | confined to epidermis, nuclear atypia | melanocyte enlargement, nuclear hyperchromasia, +/- melanocytes above suprapapillary plate (above basal layer) = "Pagetoid spread" | melanocytic hyperplasia, pagetoid Spitz nevus | Image? | Notes/other? |
| Malignant melanoma - superficial spreading type | atypical melanocytes at all levels of epidermis + dermis | atypical dermal melanocytes single, in cluster or sheets | compound melanocytic nevus | Image? | Notes/other? |
| Malignant melanoma - lentiginous type | atypical melanocytes prominent along basal keratinocytes + in dermis | nuclear atypia | DDx? | Image? | Notes/other? |
| Malignant melanoma - nodular type | dermal large nodule/sheet | nuclear atypia; may not be prominent in epidermis | metastatic melanoma | Image? | Notes/other? |
| Malignant melanoma - desmoplastic-neurotropic type AKA desmoplastic melanoma | large atypical spindle cells, btw collagen | predominantly dermal | pleomorphic undifferentiated sarcoma (MFH), scar, dermatofibroma, DFSP, leiomyosarcoma, desmoplastic Spitz nevus, sclerosing blue nevus | Image? | IHC: rarely S100-, generally Melan A- & HMB-45-; subdivided into mixed desmoplastic melanoma and pure desmoplastic melanoma |
| Malignant melanoma - nevoid type | prominent nucleoli, deep mitoses - high power diagnosis | mimics nevus at low power; "push" elastic fibers downward (unlike benign nevi) | (benign) nevus | Image? | deep HMB-45+ |
| Malignant melanoma - spitzoid type | nested pattern, nuclear atypia, no maturation (large deep cells) | NC ratio increased (vs. Spitz) | Spitz nevus | Image? | Notes/other? |
Subtypes in short
| Subtype name | Key feature |
| in situ | confined to epidermis, unlike all others |
| superficial spreading | above basal layer |
| lentiginous | along basal keratinocytes |
| nodular | nodular dermal lesion |
| desmoplastic-neurotropic | atypical dermal spindle cells |
| nevoid | nevus-like at low power |
| spitzoid | mimics Spitz nevus (at DE junction) |
Electron microscopy
- Melanosomes.
Image(s):
Stains
- Fontana-Masson stain, stains melanin.[2]
- May be useful to differentiate melanin from other brown stuff (e.g. lipofuscin, hemosiderin).
IHC
Standard panel:
- S100 +ve.
- Negative staining pretty much excludes the diagnosis.
- HMB-45 +ve -- esp. deep.
- Melan A (MART-1) +ve.
Others:
- SOX10 +ve -- useful for diff. from excision scar.[3]
- SOX-10 = pan-schwannian and melanocytic marker.
Notes:
- The standard panel above (S100, HMB-45, MART-1) is also positive in other lesions, e.g. cellular blue nevus.
See also
References
- ↑ Mitchell, Richard; Kumar, Vinay; Fausto, Nelson; Abbas, Abul K.; Aster, Jon (2011). Pocket Companion to Robbins & Cotran Pathologic Basis of Disease (8th ed.). Elsevier Saunders. pp. 595. ISBN 978-1416054542.
- ↑ URL: http://education.vetmed.vt.edu/curriculum/VM8054/labs/Lab2/Examples/exfontana.htm. Accessed on: 5 May 2010.
- ↑ Ramos-Herberth FI, Karamchandani J, Kim J, Dadras SS (September 2010). "SOX10 immunostaining distinguishes desmoplastic melanoma from excision scar". J. Cutan. Pathol. 37 (9): 944–52. doi:10.1111/j.1600-0560.2010.01568.x. PMID 20653825.