Staging of Cutaneous Melanoma

Elmore and coauthors1 present a study that evaluates the reproducibility and concordance of microstaging of melanoma using the 7th vs 8th editions of the AJCC Cancer Staging Manual.2,3 The authors report modest but significant improvements (up to 10%) in the reproducibility and concordance for both T1a and T1b or greater melanomas when categorized according to the AJCC Cancer Staging Manual, 8th edition (AJCC 8). The authors conclude that AJCC 8 will improve the accuracy of staging of invasive cutaneous melanoma and may have a positive impact on patient care. At the commencement of 2018, AJCC 8 was implemented in the United States. Among other changes, the definitions of T1a and T1b for primary cutaneous melanomas were refined from the AJCC Cancer Staging Manual, 7th edition (AJCC 7).2,3 Whereas AJCC 7 defined T1a melanomas as being of Breslow thickness 1 mm or less and lacking mitoses (defined using the dermal hotspot approach as either <1/mm2 or 1/mm2) and ulceration, AJCC 8 classifies nonulcerated melanomas less than 0.8 mm thick as T1a; T1b is defined as a melanoma 0.8 to 1.0 mm thick or less than 0.8 mm thick with ulceration. While the staging changes in AJCC 8 were data driven, the impact, if any, on reproducibility and concordance of staging was not formally evaluated by the American Joint Committee on Cancer (AJCC) Melanoma Expert Panel. Elmore et al1 evaluated the effects of the differences between the melanoma staging system in AJCC 7 vs AJCC 8 on reproducibility by analyzing a subset of data compiled from their previously published Melanoma Pathology Study.4 In the Melanoma Pathology Study, 187 pathologists evaluated 240 melanocytic lesions and classified them according to a 5-tiered system called the Melanocytic Pathology Assessment Tool and Hierarchy for Diagnosis, which includes class I, nevus or mild atypia; class II, moderate atypia; class III, severe atypia or melanoma in situ; class IV, pT1a invasive melanoma (AJCC 7); and class V, pT1b or greater invasive melanoma (AJCC 7). By analyzing the subset of 116 invasive melanomas (ie, those classified as classes IV and V by 3 expert pathologists), the authors attempted to assess the impact of AJCC melanoma staging system changes. While the study methods are not entirely clear, a significant limitation of their approach appears to be that study pathologists were tasked with scoring cases according to the Melanocytic Pathology Assessment Tool and Hierarchy for Diagnosis system, rather than focusing on classifying them into specific AJCC tumor (T) categories. Based on their classification schema, 7 T subcategories (ie, AJCC 7 T1b-T4b corresponding to Melanoma Pathology Study class V) were grouped together in the current analysis. This approach limits the reader’s interpretation of variability and reproducibility of T1b melanomas, which is important as this is a threshold at which sentinel node biopsy is often recommended.5 Another important revision in AJCC 8 was of the definition of microsatellites, which may also be associated with the reproducibility of components of the melanoma staging system. However, this was not assessed in the study by Elmore and colleagues. Microsatellites are now defined as any microscopic cutaneous and/or subcutaneous metastasis adjacent to or deep to, and completely discontinuous from, a primary melanoma with unaffected stroma occupying the space between, identified on pathological examination of the primary tumor site.2 A microsatellite can therefore upstage a patient’s melanoma to stage III. With recent clinical trial results reporting improvements in outcomes for patients with stage III melanoma receiving adjuvant systemic therapy, accurate diagnosis of microsatellites has become critical for optimal patient care.6,7 Although beyond the + Related article