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- Presentation
Diagnosis and Staging of Melanoma: Histopathology, Immunostains, Molecular Tools, and AJCC Reporting
Description
The speaker explains how melanoma is diagnosed and staged from a dermatopathology perspective, emphasizing that histopathology is the primary tool, often supplemented by immunohistochemistry and molecular testing. He stresses the importance of good clinical information and a biopsy that captures the full lesion so symmetry, circumscription, and other architectural features can be assessed. Melanoma is presented as a disease that develops through progressive genomic alterations, and pathologists try to place lesions along that biologic spectrum from nevus to invasive melanoma. Useful immunostains include p16, Ki-67, and PRAME, though none is definitive alone; PRAME is often positive in melanoma and negative in nevus, but exceptions occur. He also discusses molecular methods such as gene expression profiling, FISH, array CGH, and next-generation sequencing, which can reveal chromosomal gains and losses characteristic of melanoma and help resolve difficult cases. A case example illustrates how conflicting histology and immunostains can be clarified by sequencing, which showed mutations and copy-number abnormalities supporting melanoma. The second half covers AJCC eighth edition staging for cutaneous melanoma, including Breslow thickness, ulceration, and the definitions of T1 through T4, as well as the importance of mitotic rate and other histologic features like subtype, lymphovascular invasion, and neurotropism. Nodal staging is reviewed in terms of clinically occult versus clinically evident disease, sentinel node deposits, and the significance of microsatellites, satellites, and in-transit metastases. Overall, the talk highlights how integrated morphologic, immunohistochemical, and molecular data guide diagnosis, reporting, prognosis, and staging of melanoma.
View moreConclusions
- Primary cutaneous melanoma is best diagnosed by integrating histopathology with targeted immunohistochemistry and, when needed, molecular studies rather than relying on any single test.
- Melanoma usually shows more architectural and genomic complexity than nevus, reflecting progressive accumulation of genetic alterations over time.
- p16 loss can support melanoma by suggesting CDKN2A pathway disruption, but retained p16 does not exclude malignancy.
- Ki-67 is helpful as a proliferation marker because melanoma typically has a higher proliferative index than nevus, though exceptions exist.
- PRAME is often positive in melanoma and negative in nevus, but its imperfect sensitivity and specificity mean it must be interpreted in context.
- Gene expression profiling and genomic copy-number testing can aid difficult cases, but they are adjuncts rather than replacements for morphologic diagnosis.
- Melanoma is characterized by genomic instability and recurrent chromosomal gains and losses that are uncommon in benign nevi.
- Next-generation sequencing can demonstrate a stepwise genetic progression from benign nevus to intermediate lesions to invasive and metastatic melanoma.
- A combined interpretation of morphology, immunostains, and molecular abnormalities can resolve diagnostically ambiguous melanocytic lesions.
- Accurate melanoma staging depends heavily on Breslow thickness and ulceration, which remain major determinants of T category and survival.
- Ulceration must be identified microscopically and distinguished from artifact or trauma because it materially changes stage and prognosis.
- Mitotic rate remains an important prognostic feature even though it is no longer part of T staging, so it should still be carefully reported.
- Other pathologic features such as histologic subtype, lymphovascular invasion, and neurotropism remain clinically relevant and should be included in reporting.
- Nodal stage reflects the extent of regional disease, including sentinel node involvement and the presence of satellite, microsatellite, or in-transit metastases.
- The size and location of sentinel lymph node metastases carry prognostic and treatment implications and should be specifically documented.
- Stage III melanoma is heterogeneous, but AJCC subclassification meaningfully stratifies survival.
- The AJCC staging system for cutaneous melanoma does not apply uniformly to all melanoma sites, so site-specific staging rules matter.
- Comprehensive, standardized pathology reporting is essential because it directly informs prognosis and downstream therapeutic decisions.
- Guidelines of care for the management of primary cutaneous melanoma.
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- The Genetic Evolution of Melanoma from Precursor Lesions. New England Journal of Medicine.#10.1056/nejmoa1502583
- Minimum Pathology Reporting Elements for Melanoma: A Review of Reporting Guidelines and Proposal for Minimum Reporting Elements for a Quality Pathology Report by the Task Force of the American Society of Dermatopathology.#10.1111/cup.14848
- AJCC Cancer Staging Manual, Eighth Edition.#10.32388/xr3rjy
- Gershenwald JE et al. CA Journal Clinic. 2017. 67(6):472-492.