Resident, PGY VI Yale School of Medicine, United States
Disclosure: Disclosure information not submitted.
Participants should be aware of the following financial/non-financial relationships:
Catherine L. Ly, MD: Disclosure information not submitted.
Introduction: Mitotic rate (MR) is considered to be an important prognostic factor for melanoma, but is not utilized in the current staging system because its nuanced effect on outcomes is not yet clearly delineated. In this study, we sought to determine if elevated MR is predictive of sentinel lymph node (SLN) positivity, recurrence, and melanoma-associated death.
Methods: A retrospective review of patients diagnosed with primary cutaneous melanoma from January 1994 to August 2020 at a single academic center was performed. Breslow thickness, ulceration, MR, SLN positivity, recurrence, and cause of death (if applicable) were recorded. Based on prior literature, MR was considered elevated for each AJCC8-defined T category if it was ≥2 mitoses/mm2 for T1, ≥4 for T2, ≥6 for T3, or ≥7 for T4. Statistical analysis was performed to assess the effect of MR on outcomes independent of ulceration.
Results: A total of 2,984 patients had complete data for analysis. Elevated MR was independently predictive of death (HR 1.44, P=0.018), but not as much so as thickness (HR 2.62, P< 0.0001) or ulceration (HR 1.67, P=0.0015). There was no difference among patients with ulcerated T1 tumors regardless of MR, but those with non-ulcerated T1 tumors and elevated MR were more likely to have positive SLNs (P< 0.0001) and recurrence (P=0.0007) compared to those with low MR. Among these patients, 51.5% underwent SLN biopsy with a 14.1% positivity rate. Of those who did not undergo biopsy, 2.5% developed nodal recurrence and 2.5% were found to have distant disease. Elevated MR was similarly predictive of SLN positivity (P=0.0043) and recurrence (P=0.0004) for those with non-ulcerated T2 tumors. These patients had a 23.7% SLN biopsy positivity rate and, of those without biopsy, 21.1% recurred in nodes and 21.1% distantly. There were no notable differences for T3 or T4 tumors based on MR.
Conclusions: Elevated MR is associated with an increased risk of SLN positivity and recurrence in thin melanomas, independent of ulceration. SLN biopsy should therefore be strongly considered for patients with non-ulcerated lesions if the MR is ≥2 mitoses/mm2 for those with T1 tumors or ≥4 for T2 tumors.
Learning Objectives:
Identify a means by which to incorporate mitotic rate into the melanoma staging system
Develop an understanding of how mitotic rate can affect outcomes in melanoma
Utilize mitotic rate as a component of the decision-making progress when it comes to determining whether sentinel lymph node biopsy is recommended for thin melanomas
