AIMS: Subareolar sclerosing ductal hyperplasia (SSDH) is a distinct type of complex sclerosing hyperplastic lesion first described by Rosen in 1987. There have been rare studies investigating SSDH; however, no genetic study has been performed to date. METHODS AND RESULTS: Seven SSDH cases, diagnosed between 2013 and 2024, were identified. All were subjected to next-generation sequencing (523 genes). Patient ages ranged from 40 to 74 years (median = 46). All lesions were located in the subareolar region. Each showed the characteristic appearance of the lesion, as described in the seminal study, with usual ductal hyperplasia in a densely sclerotic background imparting an 'infiltrative' appearance. None of the cases showed atypical hyperplasia or carcinoma. DNA sequencing identified PI3K pathway alterations in all seven cases: PIK3CA (n = three, one with two alterations), PIK3R1 (n = three) and PIK3C3 (n = one, with concurrent FAT1 mutation). CONCLUSION: SSDH shows PI3K pathway alterations similar to those seen in other non-atypical and atypical proliferative lesions as well as benign and malignant neoplasms of the breast. This finding may explain the rare association of SSDH with atypical hyperplasia, in-situ and invasive carcinoma.
