OBJECTIVE:The objective of our study was to evaluate the outcome of lobular neoplasia diagnosed at 11-gauge stereotactic vacuum-assisted biopsy (SVAB). MATERIALS AND METHODS:Retrospective review of 1,819 lesions sampled with 11-gauge SVAB yielded 27 patients with lobular neoplasia as the most severe pathologic entity diagnosed. Patients with lobular neoplasia associated with atypical ductal hyperplasia (ADH), ductal carcinoma in situ (DCIS), or infiltrating carcinoma were excluded. Twenty patients underwent surgical excisional biopsy, and seven patients were followed mammographically for a mean of 52 months (range, 14-67 months). Mammographic lesion type, number of specimens obtained per lesion, and specific histologic features related to lobular carcinoma in situ (LCIS) were assessed. Results were compared with histologic findings at surgery or mammographic follow-up. RESULTS:Nineteen lesions presented mammographically as microcalcifications, four as masses, three as masses with associated microcalcifications, and one as architectural distortion. A mean of 13 specimens were obtained per lesion. Carcinoma was found at surgical excision in 19% of the lesions (5/27). Lesions were upgraded to DCIS (n = 2), invasive lobular carcinoma (n = 2), and mixed invasive ductal and lobular carcinoma (n = 1). In addition to the diagnosis of lobular neoplasia at SVAB, one patient presented with synchronous infiltrating ductal carcinoma in the contralateral breast, and two patients developed metachronous infiltrating ductal carcinoma in a different quadrant of the ipsilateral breast. Twelve of the 27 lesions included LCIS. These lesions were evaluated pathologically to distinguish the classic (10/12) from the pleomorphic (2/12) form of this entity. Ten of the 12 LCIS cases underwent surgical excisional biopsy with four of the five upgrades occurring in these patients. Only one of these patients was shown to have the pleomorphic type of LCIS. Lesions in seven patients who underwent mammographic follow-up remained stable. CONCLUSION:The known association of lobular neoplasia with high-risk and malignant lesions at surgical biopsy requires careful consideration when lobular neoplasia is diagnosed as the most severe histologic entity at SVAB. The diagnosis of lobular neoplasia at 11-gauge SVAB is not reliable in view of the 19% upgrade rate at the time of surgical excisional biopsy in our study. No predictive mammographic features allowed distinction between the patients with lesions that were upgraded at the time of surgery from those whose lesions were not upgraded.