Pleomorphic lobular carcinoma in situ (PLCIS) is an aggressive subtype of lobular carcinoma in situ treated similarly to ductal carcinoma in situ. The purpose of this study was to determine the imaging findings, upgrade rate of PLCIS at core needle biopsy (CNB), and the treatment and outcomes of these patients.

This retrospective single-institution study included women with PLCIS at CNB or excisional biopsy without concomitant DCIS or invasive carcinoma between January 1, 1999, and July 20, 2016. Imaging findings, detection mode, treatment, and outcomes were reviewed. Retrospective review of the images was performed. Upgrade rate to ductal carcinoma in situ or invasive carcinoma at lumpectomy was calculated.

Twenty-one patients had a finding of PLCIS at CNB (n = 16) or excisional biopsy (n = 5). Four of 15 (27%; 95% CI, 4-49%) cases of PLCIS at CNB were upgraded to DCIS (two cases) or invasive lobular cancer (two cases) at lumpectomy (one patient declined excision). No unique mammographic features were predictive of need to upgrade or extent of disease. Among the patients with pure PLCIS (not upgraded), 13 of 16 (81%) presented with fine pleomorphic calcifications on screening mammograms, 1 of 16 (6%) with distortion and calcifications, 1 of 16 (6%) with a mass, and 1 of 16 (6%) with nonmass enhancement at MRI. The median imaging size was 11 mm (mean, 14 mm; range, 3-47 mm). Twelve of 16 (75%) patients were treated with lumpectomy and 4 of 16 (25%) with mastectomy. Eight of 16 (50%) patients received adjuvant hormonal therapy, and 2 of 16 (17%) received radiation. There were no local recurrences.

PLCIS most commonly presented as fine pleomorphic calcifications on mammograms and had a high upgrade rate after CNB. CNB diagnosis of PLCIS requires surgical excision.