Syringocystadenoma Papilliferum Concurrently Presenting with Tubular Apocrine Adenoma on the Back: A Rare Combination

Dear Editor, The patient is a 2-year-old boy who presented with a pink, itchy plaque on his back that had persisted for 2 years. He had a single papule on his back since birth, which gradually enlarged and became associated with itching. There was no family history of or history of insect bites. A dermatological examination revealed a well-defined, pink, band-like plaque measuring approximately 2 cm × 0.8 cm. This plaque was composed of clustered papules with central umbilication along the midline of the back, with the long axis of the lesion parallel to the spine [Figure 1]. Histopathological analysis showed mild epidermal hyperplasia with numerous cysts extending into the dermis [Figure 2a]. The cysts displayed a bilayered glandular epithelium, consisting of tall columnar cells in the inner layer that secrete apocrine material, and small cuboidal cells with deeply stained nuclei in the outer layer. There was significant infiltration of plasma cells within the stromal tissue of the neoplasm [Figure 2b]. In the lower portion of the lesion, cystic and branching tubular structures of varying sizes were observed [Figure 2c]. These structures exhibited double or multiple layers of epithelium, with cells lining the lumen showing evidence of apocrine secretion [Figure 2d]. The upper part of the lesion displayed typical features of syringocystadenoma papilliferum (SCAP), while the lower part was consistent with tubular apocrine adenoma. The entire lesion was surgically removed, and there has been no recurrence during the one-month follow-up.Figure 1: Pink plaque with small nodules arranged linearly on the backFigure 2: Histomorphologic features. Mild epidermal hyperplasia with sunken cysts in the dermis (a, H and E ×40). Papillary structures extending into the cysts are edged by two types of cells (b, H and E ×400). Papillary structures in cysts lined by two cell types (c, H and E ×40). Tubular structures with double or multi-layered epithelium (d, H and E ×400)SCAP is a relatively rare benign adnexal neoplasm of the skin. Approximately 50% of patients present with SCAP at birth, while 15%–30% develop it before adolescence, often experiencing rapid enlargement during puberty.[1] The tumour most commonly affects the scalp, followed by the trunk and extremities. In contrast, tubular apocrine adenoma (TAA) is an uncommon benign tumour of the sweat glands, predominantly seen in middle-aged individuals, with a higher incidence among women. TAA typically appears as an asymptomatic solitary nodule, most frequently on the scalp. In 1987, Toribio et al.[2] first reported the association between SCAP and TAA. Subsequent studies confirmed the morphological similarities between these two conditions but even experienced dermatopathologists and pathologists have not established universally accepted diagnostic criteria. Kazakov et al.[3] proposed that TAA may transform into SCAP through ulceration when communicating with the external environment, while lesions without such communication retain TAA characteristics. However, Ishiko et al.[4] classified TAA as a distinct entity after reviewing 19 documented cases. They identified several key differences between SCAP and TAA: (1) TAA does not exhibit cystically dilated apocrine invaginations extending from the epidermis; and (2) papillary projections are not present. Recognizing SCAP and TAA as separate entities aligns with the definition of collision tumours, which refers to the coexistence of two different tumours within a single biopsy specimen.[5] Nevus sebaceous is the most commonly associated lesion with SCAP and TAA; however, the excised specimen in our case showed no evidence of a pre-existing nevus sebaceous. SCAP alongside TAA without a nevus sebaceous is sporadic and sometimes arises in unusual locations. This case represents the tenth instance reported worldwide [Table 1].Table 1: Review of cases of SCAP and TAA in the absence of nevus sebaceusDeclaration of patient consent The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.