While there is little consensus on the ideal role of immunohistochemical (IHC) stains in the diagnosis of melanoma, their use increased dramatically over a 15-year period, according to results from a study.
Randie H. Kim, MD, PhD, and Shane A. Meehan, MD, of New York University, reviewed nearly 6,300 pathology reports from patients with melanomas, all referred (along with tissue samples) to their center from other institutions during 2001-2015. One or more IHC stains were used diagnostically in 871 cases during the study period, with use increasing from 5% of patients in 2001 to 25% in 2015 (P less than .0001). Usage increased gradually over time, although the number of stains used per case did not increase significantly (J Cutan Pathol. 2017 Mar;44[3]:221-7).
IHC stain use was associated with melanomas occurring on the head or neck (odds ratio = 1.6; 95% confidence interval, 1.4-1.9), acral melanomas (OR = 1.5; 95% CI 1.1-2.0) and melanomas thicker than 4 mm (OR = 2.5; 95% CI 1.7-3.6). The most common stain used in the study was Melan-A/MART-1 (melanoma antigen recognized by T cells), the most specific of the IHC markers available and the one “largely responsible for the increased incidence in overall immunostain use in our study,” the researchers wrote. “The perception that melanocytic markers, such as Melan-A, can more accurately stage melanomas, is a potential explanation for its increased usage over the duration of the study period.”
The higher use of immunostains in thicker melanomas may be because these “exhibit greater morphological heterogeneity, such as nodular, spindled and desmoplastic subtypes, that lead to additional confirmational testing,” Dr. Kim and Dr. Meehan noted. However, they cautioned that extrinsic factors, including reimbursement fees and concerns about malpractice claims, could also influence the use of IHC stains in the diagnosis of melanomas.
“While Melan-A/MART-1 is a useful adjunct for determining melanocytic density or the presence of invasion in difficult cases, its routine use on melanomas has not been validated,” the researchers wrote in their analysis. “A consensus conference delineating the appropriate use of IHC in the diagnosis of melanoma may be of value in this regard.”
Dr. Kim and Dr. Meehan also noted that while a greater proportion of the melanomas seen in the study were thick (greater than 4 mm) compared with most population-based studies, this may reflect patient management practices in which thinner melanomas are treated in outpatient centers while thicker ones get referred to tertiary care centers such as theirs.
The researchers disclosed no outside funding or conflicts of interest.