Preoperative MRI for pleomorphic lobular carcinoma in situ: Implications for surgical management

Background Pleomorphic lobular carcinoma in situ (PLCIS), a more aggressive variant of classic LCIS (CLCIS), demonstrates higher rates of upgrade to invasive carcinoma at surgical excision. Mammography may underestimate disease extent, whereas MRI may delineate lesions due to sensitivity. Methods Our institutional pathology database was queried for patients diagnosed with PLCIS on core needle biopsy (CNB) from 2002 to 2025 who underwent surgical excision. Preoperative MRI and MRI-guided biopsies were reviewed. Radiologic, pathologic, surgical, and outcome data were collected. Proportions were summarized with 95% confidence intervals. Fisher's exact test assessed associations between categorical variables, and Bayesian logistic regression evaluated the relationship between calcification size and malignant upgrade. Results Preoperative MRI was performed in 94.7% (18/19) of patients. Among these, 61.1% (11/18) underwent additional biopsy, identifying additional LCIS in 72.7% (8/11), benign findings in 18.2% (2/11), and malignancy in 9.1% (1/11). Mammographic PLCIS presentation included calcifications (26.3%), mass (5.3%), both (31.6%), or neither (36.8%). Among cases with calcifications, 45.5% (5/11) upgraded to malignancy. Increasing calcification size was associated with higher upgrade probability (OR 1.32 per cm, 95% CrI: 0.68–2.97), increasing from 35% at 0.5 cm to 52% at 3.0 cm. The overall upgrade rate was 47.4% (9/19). Conclusion Preoperative MRI in PLCIS frequently prompts additional biopsies, often detecting further LCIS rather than malignancy. Calcification extent predicts upgrade, and the high upgrade rate supports surgical excision after CNB diagnosis.