Abstract Background Encapsulated Apocrine Papillary Carcinoma (EAPC) of the breast are very rare tumors. They usually present as a cystic mass with mural nodule in women aged 44–84 years. Affected patients may be asymptomatic or complain of breast swelling, or nipple discharge. Mammographic features are nonspecific. The tumor appears as a high-density round or oval mass with circumscribed or spiculated margins on mammography. On Ultrasonography (US) a classical lesion appears as predominantly cystic mass with intracystic solid papillary projections and area of vascularity within it. Contrast Enhanced Breast MRI helps to further characterize the lesion by showing intense contrast enhancement in early phase along with washout curve. Histological features of these tumors are similar to those of classical encapsulated papillary neoplasm, in that myoepithelial cells are absent within the papillary structures and at the periphery of the cyst. They show variable degree of cytological atypia and mitotic activity. Such tumors consist of abundant granular eosinophilic cytoplasm and large nuclei with prominent nucleoli and are androgen receptor positive. However, a multidisciplinary approach is crucial for diagnosis and tissue histology is essential to suitably formulate treatment guidelines. Surgical excision is the preferred treating option for these tumors. Little consensus is available about local radiation and adjuvant therapy for the treatment of such tumors, yet they have been reported to have good prognosis. Case presentation This rare case report describes the intriguing journey towards the diagnosis of an encapsulated intracystic apocrine papillary carcinoma in a 52-year-old premenopausal female who presented with palpable breast swelling in left breast. The patient underwent mammography, breast ultrasound and breast MRI concluding it to be a BIRADS 4A lesion. Then the patient was subjected to trucut core biopsy and finally surgical excision was performed. On Histopathology this lesion was diagnosed as encapsulated apocrine papillary carcinoma with androgen receptor positivity and triple negative hormonal status. At present patient is on regular follow-up. Conclusions Encapsulated intracystic apocrine papillary carcinoma has a favorable prognosis with low recurrence rate and excellent long-term survival regardless of its invasive nature. Therefore, we present this rare entity to highlight the importance of radiological and histopathology findings in its diagnosis.
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