Adenomatous eccrine metaplasia--a novel reaction pattern

We recently observed atypical adenomatous metaplasia of eccrine glands in an excisional biopsy of squamous cell carcinoma (SCC). This led us to this study in an effort to ascertain whether this reaction pattern is common to all excisional biopsies and, depending on its presence in association with residual tumor, whether it is lineage specific. We performed a retrospective review of 201 excisional biopsies and noted that adenomatous metaplasia was present in 35 of 201 (17%) of the cases, of which 19 had residual tumor. Adenomatous metaplasia seemed to be more frequent in epithelial neoplasms such as basal cell carcinomas 15 of 94 (16%) and SCCs 13 of 61 (21%) although only (3 of 41) 7% of nevomelanocytic proliferations exhibited this change. Residual tumor was noted in association with adenomatous metaplasia, in 11 of 15 cases (73%) in the basal cell carcinoma subgroup, in 8 of 13 cases (62%) in the SCC subgroup, and in none from the nevomelanocytic subgroup. Comparing frequencies of adenomatous metaplasia across groups, only SCC specimens with residual tumor demonstrated a statistically significant increase compared with nevomelanocytic neoplasm (35% vs. 7%, P = 0.01). Findings from the current study expand the spectrum of metaplastic change involving eccrine glands to include adenomatous metaplasia. Given that it seems to be more common to epithelial malignancies, it seems reasonable to posit that this reaction pattern is the consequence of hitherto undefined proteins induced by epithelial tumor cells resulting in exuberant stimulation of eccrine glands, although immunohistochemical and molecular studies are required to define the precise cause.