Mixed Tumor, Eccrine Type: So What If it’s Vulval!

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To the Editor:
We read with great interest a case report by Rajguru et al. 1 titled “Vulval microglandular adenosis (MGA)-like neoplasm with chondromyxoid stroma: report of a unique case.” We received an identical tumor in the vulval skin excised from a 58-year-old woman. A differential diagnosis we considered for this tumor was MGA arising from the anogenital mammary-like glands. As we work in a dermatopathology practice, we do not subscribe to the International Journal of Gynaecological Pathology and consequentially we were unaware of the recent report of MGA-like neoplasm in vulva when we formulated the differentials. We were excited to find this recent case report as it potentially mirrored our thoughts. However, further stains and review led us to correctly classify this neoplasm as a mixed tumor of eccrine type, a monophasic variant of chondroid syringoma.
Like the neoplasm described by Rajguru et al. 1, our tumor was well circumscribed, however, unlike the former it was excised with the surrounding dermis (Fig. 1). The tumor had a compressed tissue capsule and was composed of small tubules and ducts lined by a single layer of cells. These cuboidal cells show eosinophilic to clear vacuolated cytoplasm and round, central, bland nuclei (Fig. 2). The nuclei show small nucleoli, fine chromatin, and occasional inclusions (inset Fig. 2). The stroma was myxoid and stained blue with Alcian blue (Fig. 3A). Tubular lumens predominantly contained bluish bubbly material. However, focally there was pink material in the lumens that stained positive with DiPAS (Figs. 2, 3A). The tumor cells stained diffusely and strongly positive for CK7 (Fig. 3B) and S100 (Fig. 3C). The stains for p63 (Fig. 3D), Melan A and SMA were negative. Ki67 was <2%. These findings were consistent with those depicted in the case report by Rajguru et al. 1 and those described for mixed tumor, eccrine type by Kazakov et al. 2.
Rajguru et al. 1, rightly generated the differential of a chondroid syringoma, but ruled it out based on the absence of myoepithelial cells. However, Rajguru et al. 1, failed to evaluate the full spectrum of mixed tumors of the skin especially the so called eccrine variant. This tumor, unlike the more common apocrine mixed tumor, is single layered and devoid of myoepithelial cells histologically and immunohistochemically. The absence of myoepithelial cells is consistent with the diagnosis of a mixed tumor of eccrine type. Moreover, it is unlikely for even a benign MGA to be well circumscribed and chondromyxoid stroma has been reported in benign MGA but it is uncommon 3–5. Presumably for the latter 2 reasons Rajguru et al. 1 named their tumor as MGA-like and not purely MGA.
When faced with tumors in special sites such as the vulva, the question one needs to ask is this: “If this tumor would have occurred at any other site in the skin and would be labeled mixed tumor of eccrine type, then does its occurrence in vulval skin necessitate a separate designation even when the presence of anogenital mammary-like glands is not evident?” The answer for us was “no” and hence we prefer to designate this tumor as mixed tumor of eccrine type. Moreover, there are no anogenital mammary-like glands in the head and neck or scalp where this tumor occurs most commonly and a designation of MGA or its look-alike would not be justifiable at these sites. Indeed we have encountered identical mixed tumors of eccrine type elsewhere in the body and one such tumor is depicted in Figure 4 from the scalp of a 67-year-old man.
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