How does the mitotic index impact patients with T1 melanoma? Comparison between the 7th and 8th edition of the American Joint Committee on Cancer melanoma staging system

Abstract

Background The mitotic index is no longer used to classify T1 melanoma patients into T1a and T1b, so it should not be used to indicate sentinel node biopsy in these patients. Objectives To evaluate patients with T1 melanoma who underwent sentinel lymph node biopsy and to compare those who were classified as T1a with those classified T1b, according to the 7th and 8th Edition of the melanoma staging system, regarding a positive biopsy result. The authors also aimed to assess whether there is any difference in the results in both staging systems. Material and methods This was a retrospective analysis of 1213 patients who underwent sentinel lymph node biopsy for melanoma, from 2000 to 2015, in a single institution. Results Of 399 patients with thin melanomas, 27 (6.7%) presented positive sentinel lymph nodes; there was no difference in positivity for sentinel node biopsy when comparing T1a vs . T1b in both staging systems. Furthermore, the clinical results were also similar between the two groups. However, in the complete cohort analysis, the mitotic index was associated with positivity for sentinel lymph node biopsy (p < 0.0001), positivity for non-sentinel lymph node (p < 0.0001), recurrence-free survival (p < 0.0001), and specific melanoma survival (p = 0.023). Study limitation Unicentric study. Conclusion The mitotic index was shown to be a very important prognostic factor in the present study, but it was not observed in patients classified as T1. The mitotic index should no longer be used as the only reason to refer sentinel lymph node biopsy in patients with thin melanoma.

More sentinel lymph node biopsies for thin melanomas after transition to AJCC 8th edition do not increase positivity rate: A Danish population‐based study of 7148 patients

“…When pooling all T1 melanomas undergoing SLNB in the whole period, our results strongly indicate that the presence of mitoses in thin melanomas increases the risk of +SLN, which is in agreement with several other studies 14,15,17,19,21,31,32 ; in the largest meta‐analysis (from 2016) to date within this topic, evaluating 60 studies, MR was found to be the strongest predictor of +SLN in thin melanoma 21 . Some studies, however, do not find MR as a predictor of +SLN 28–30,33–36 …”

“…The +SLN rates of 6.7% (AJCC7 cohort) and 4.7% (AJCC8 cohort), respectively, concur with previous retrospective studies 14–16,19,21,28–31 . Our results indicate that performing SLNB in patients with thin melanomas based solely on the AJCC T1b subcategory is problematic as it relies on a small set of criteria, causing a substantial risk of both over‐ and undertreatment 14,30 ; in an Italian retrospective multicenter study of 1272 T1 patients undergoing SLNB, Piazzalunga et al 30 found that even though the AJCC8 resulted in a reduction of T1a patients with +SLN compared with previous AJCC editions, the T1a patients still constituted 10.7% of all +SLN patients.…”

“…It is important to note that most studies, both those confirming and those conflicting with our findings, used several different statistical analyses, different methods of quantifying MR and were mainly retrospective with smaller sample sizes, which may explain the discrepancy. Nevertheless, when melanomas of all thicknesses are considered, MR has shown to be associated with both +SLN rate and melanoma‐specific survival 1,18,28,36,37 . Although not included in the AJCC8, the AJCC Committee acknowledges the value of MR and recommends continued reporting of MR for all primary melanomas 1 …”

Macroscopic tumor dimension, sentinel lymph node outcome, and survival analysis among cutaneous melanoma

“…9,10 Other features for prognostic evaluation include the presence or absence of ulceration, lymphovascular invasion, lymphocytic infiltrate, regression, satellites, mitotic index, and histological subtype. [11][12][13][14][15][16][17][18] The tumor dimension is a parameter for staging squamous cell carcinoma and uveal melanoma, but not for cutaneous ª 2024 the International Society of Dermatology.…”

“…This system defines pathological staging (T), excision margin size, and sentinel lymph node applicability 9,10 . Other features for prognostic evaluation include the presence or absence of ulceration, lymphovascular invasion, lymphocytic infiltrate, regression, satellites, mitotic index, and histological subtype 11–18 …”