Abstract

Introduction: Given the broad differential diagnosis of pagetoid lesions of the breast, immunohistochemical stains are routinely used to aid in correct diagnosis. While IHC is an important component of the histopathologic workup, it can easily lead to diagnostic error without correct interpretation. We present a case of SOX-10 positive mammary Paget’s disease, highlighting a potential pitfall when interpreting immunohistochemical markers for pagetoid lesions of the breast. Case A 61 year old female with a history of stage I invasive ductal carcinoma of the right breast (ER-/PR-/HER2-) presented with skin changes overlying the right nipple. A punch biopsy was obtained, revealing numerous atypical epithelioid cells within the epidermis with distinct intraepidermal scatter. The lesional cells labeled with CK7, Cam5.2, GATA-3. and SOX-10. Negative stains included MART-1, HMB-45, ER, PR, and HER2. A diagnosis of Paget disease was rendered. Discussion: SOX-10 has been reported in the literature as a useful marker for triple negative breast cancer. Positivity in our present case is likely due to the patient’s known history of triple negative invasive ductal carcinoma. SOX-10 positivity in the setting of a pagetoid lesion of the breast has potential for misdiagnosis as a melanocytic lesion if additional history and supporting immunostains are not considered. This is particularly important in cases of CK7-negative Paget disease. Conclusion: SOX-10 should not be used in isolation when considering melanoma in the differential diagnosis of a pagetoid lesion. Sox-10 has been reported in the literature as a sensitive marker for triple negative breast cancer, and positivity should direct further immunohistochemical and clinical work-up.

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