To the Editor
Apocrine tubular adenoma (TA) is a rare cutaneous neoplasm that was first described by Landry and Winkelmann (1) in 1972. Tubular adenoma is usually located deeply within the dermis of the scalp region and commonly presents as a painless skin nodule. Histologically, TA overlaps with both papillary eccrine adenoma and syringocystadenoma papilliferum (SAP), to the extent that it may be considered as a histological continuum between these 2 lesions.
We report a case of TA in a very unusual location. To the best of our knowledge, it has not been previously described in the vulva.
A 58-year-old woman presented with a painless mobile cutaneous mass involving the left labia of unknown duration. There was no associated regional lymphadenopathy. The lesion was treated by simple excision. The patient received no further therapy and was well during the 1-year period of follow-up.
Gross appearance revealed a well-circumscribed nodule measuring 1.0 × 1.0 × 1.0 cm. Microscopically, the mass showed a multilocular cystic nodule with intraluminal papillary projections devoid of stromal cores (Fig. 1). Some of the cystic spaces showed squamous metaplasia. Elsewhere, the tumor showed classic double-layered epithelium with an inner lining of tall columnar cells and outer flattened cells. The former showed decapitation secretion (Fig. 2). In addition, focal ductal differentiation was noted. The intervening stroma was scanty and fibrous with minimal inflammatory cells devoid of plasma cells. There was no evidence of comedolike channels, hyaline, or clear cell differentiation. Immunohistochemistry showed restricted carcinoembryonic antigen (CEA) (Fig. 3), CK7, and gross cystic disease fluid protein 15 expression to the luminal cells. AE1/AE3, cell adhesion molecule 5.2, and CK5 and 6 were diffusely expressed in both the peripheral and luminal cells.
Tubular adenoma is a rare sweat gland tumor that exhibit apocrine differentiation. The most common location is in the scalp. Rarely, it has been described in other locations such as the eyelid (2), chest (3), external auditory meatus (4), cheek (5), and axilla (6).
Histologically, TA is characterized by lobules of well-differentiated tubular structures located in the dermis. The tubules are lined by an outer layer of tall columnar cells and an inner cuboidal cell layer, showing decapitation. Connection with the overlying epidermis by 1 or more ductlike structures is often observed. Occasionally, comedolike channels that extend into the epidermis and connect with some of the tubular structures are seen (1). In the present case, the tumor relation to the overlying epidermis was precluded because the tumor was managed by simple enucleation.
One of the characteristic morphological features of TA is having cells with apocrine differentiation. Such differentiation is well documented by ultrastructural studies and immunohistochemistry. The former shows the luminal cells to have vacuoles, lipid granules, and microvilli that project into the lumen of the tubules (7). Immunoperoxidase studies have shown tumor cells expressing cytokeratins, estrogen receptors (8), and gross cystic disease fluid protein 15. Carcinoembryonic antigen was found predominantly in the lumen of the ducts and in the apical portion of the luminal cells (8,9). This pattern is similar to the distribution described in normal sweat glands (8).
Tubular adenoma has been reported to occur within a mammary adenoid cystic carcinoma (10) and in association with papillary eccrine adenoma (11), but the most common association is with SAP (3,9,12). In the latter setting, they are usually preceded by an organoid nevus (12). Hence, TA and SAP might represent a spectrum of single disease (12). In addition to the common association, the 2 tumors often overlap because they show similar clinical, morphological, and immunophenotypic features. The localization to the scalp, the nodular and lobulated appearance, and the apocrine structures indicate that this tumor is similar to SAP and must be differentiated from it (7). In contrast to TA that is usually located within the deep dermis and composed of fibrous stromal tissue with few inflammatory cells predominantly of lymphohistiocytic type. Syringocystadenoma papilliferum is often located in the upper dermis and shows stroma with prominent inflammatory infiltrate with plasma cell predominance. In addition, TA neither shows cystically dilated invaginations nor papillary projections. Although the immunophenotype of both lesions overlaps, the presence of S-100 protein expression within the peripheral cells is a feature of TA rather than SAP (9).
Generally, TA is considered as benign neoplasm; however, it may behave in a locally aggressive manner (7). The presence of several characteristics may suggest that this tumor may not behave in an entirely benign fashion. These characteristics include bridging of the luminal cells, calcification, slight cellular atypia, poorly delineated tumor lobules, and perineural invasion (7,12). In such setting, it may be difficult to differentiate apocrine TA from metastatic adenocarcinoma or apocrine carcinoma (12). Worrisome features were not present in our case. Some investigators have concluded that, even in the absence of cellular atypia, TA may behave clinically in a quietly aggressive fashion and therefore warrant treatment as a locally aggressive malignancy (13).
Although the mostly acceptable treatment for TA is simple surgical excision, successful management of the tumor using the Mohs technique has been reported (5). The latter treatment has been justified for cases in which the margins of the tumor are ill defined. In our case, the treatment was simple surgical excision with no further treatment.
Dina El Demellawy, M.D., Ph.D., F.R.C.P.C.
Department of Pathology and Laboratory Medicine
Northern Ontario School of Medicine
West Campus, Thunder Bay
Dean Daya, M.D., F.C.A.P, F.R.C.P.C.
Salem Alowami, M.B., B.Ch., F.C.A.P., F.R.C.P.C.
Department of Pathology and Molecular Medicine
This study satisfies the ethical requirements of the Research Ethics Board, Hamilton Health Sciences/Faculty of Health Sciences, McMaster University, Hamilton, Ontario, Canada.
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