DP26 Syringocystadenocarcinoma papilliferum masquerading as squamous cell carcinoma

Abstract

Abstract Syringocystadenocarcinoma papilliferum (SCACP) is a rare cutaneous adnexal neoplasm with ~30 cases reported. This case highlights the potential diagnostic and treatment challenges. A 52-year-old woman presented with a poorly differentiated carcinoma on the left parietal scalp which recurred 2 and 5 years following the original surgical excision. Initial biopsy of this lesion had shown syringocystadenoma papilliferum (SCAP) with associated syringoma, and a subsequent wider excision revealed suspected poorly differentiated squamous cell carcinoma (SCC) in the deeper dermis that was fully excised; however, the SCAP reached the margins. Excision 2 years later of the first recurrence showed similar histological features, and a second recurrence was excised twice to achieve histological clearance followed by postoperative radiotherapy. She remains tumour-free 2 years later. Upon retrospective review of all specimens, the initial primary tumour excision showed histological findings of a surface exophytic SCAP with mild nuclear enlargement, nucleoli and scattered mitotic figures. An infiltrative lesion was seen beneath this consisting of atypical ductal structures within a fibroblastic stroma. In deeper regions, there was more solid proliferation with some squamous differentiation, although scattered glandular units remained visible. However, the squamous component was predominant in future biopsies and even represented the sole morphological appearance in some. This culminated in the latest biopsy showing a poorly differentiated spindle cell tumour which, with immunohistochemistry (BerEP4-negative; cytokeratin, CK14−, CK5−, p63− and p53-positive; and high Ki67 index), was considered entirely to be a poorly differentiated SCC. Ultimately, this sequence of biopsies actually represented the rare diagnosis of SCACP, which demonstrated progressive squamous differentiation with each recurrence. A previous case published also reported SCACP transition to squamous differentiation (Zhang YH, Wang WL, Rapini RP et al. Syringocystadenocarcinoma papilliferum with transition to areas of squamous differentiation: a case report and review of the literature. Am J Dermatopathol 2012; 34:428–33). Despite the generally favourable prognosis reported, there have been a few cases of locoregional metastasis. Furthermore, recurrence up to 8 years after excision of the primary tumour has been reported (Castillo L, Moreno A, Tardío JC. Syringocystadenocarcinoma papilliferum in situ: report of a case with late recurrence. Am J Dermatopathol 2014; 36:348–52). We present a unique case of doubly recurrent SCACP managed with surgery and adjuvant radiotherapy which highlights the need for long-term follow-up. Furthermore, SCACP may pose a diagnostic challenge due to squamous differentiation of these tumours, which may result in incorrect or delayed diagnosis.