Incidence and Risk Factors for Incidental Cancer on Melanoma Wide Excisions

Cancer patients and survivors have a high risk of developing additional malignancies. Patients who undergo melanoma excision often have sun-damaged skin and are predisposed to concurrent and subsequent skin cancers. The unexpected finding of an incidental cancer on melanoma wide excisions can require further surgery and delays adjuvant treatment. We aimed to determine the incidence and risk factors for incidental skin cancers in patients who had surgical excision of melanoma.

Our single-center retrospective study analyzed all patients diagnosed with primary melanoma at our institution from July 1, 2019 through June 30, 2020. We included patients with localized cutaneous melanoma who underwent surgical excision and had relevant pathology data available. Descriptive statistics and univariate analyses were performed on the demographic, clinical, and pathological data collected. We analyzed differences between the groups with and without incidental cancer to ascertain risk factors using chi-squared tests and Wilcoxon rank sum tests. Dunn's tests with Bonferroni correction were performed for multiple pairwise comparisons.

There were 642 patients who met the criteria for inclusion, of whom 13 (2.0%) had incidental cancers identified on a pathologic assessment. Six (46%) had incidental squamous cell carcinoma and seven (54%) had basal cell carcinoma. With regard to management of incidental cancer, three (23%) patients required additional surgery for margin re-excision. Risk factors for incidental cancers in melanoma excision included older age (median 79 versus 62 y, P < 0.001), male sex (P = 0.042), and primary tumor location in the head/neck region relative to trunk (P < 0.01) or extremity (P < 0.01) primary sites.

Although the frequency of incidental findings on melanoma excision is low, certain patients are at a greater risk including older male individuals with head/neck melanomas. These findings can be used to improve preoperative counseling of at-risk patients when melanoma excision is planned.