Clinical management and oncologic outcomes of pure pleomorphic and florid lobular carcinoma in situ of the breast: Results from a large single institution experience

Introduction: Pure pleomorphic (PLCIS) and florid (FLCIS) lobular carcinoma in situ, without concurrent invasive carcinoma (IC) or ductal carcinoma in situ (DCIS), are rare. We collected the largest and most comprehensive single-institution cohort to analyze oncological outcomes and management strategies. Methods: Consecutive patients diagnosed with pure PLCIS and/or FLCIS and treated at our institution between 2012 and 2021 were identified. Clinical, radiological, and pathological characteristics, along with recurrence risk, were analyzed. Results: A total of 303 patients were diagnosed with PLCIS and/or FLCIS on surgical specimens. Among them, 144 PLCIS and 116 FLCIS cases were associated with IC or DCIS, leaving 43 (14.2 %) pure P-/FLCIS cases (20 PLCIS, 17 FLCIS, and six mixed cases). Pure P-/FLCIS diagnosed on core-biopsy had a 31.3 % upgrade ratio on surgical specimens to IC (86.7 %) or DCIS (13.3 %). Median lesion size was 15 mm. Mastectomy was performed in four cases, while 90.7 % underwent wide local excision, with 14 % positive margin rate. Sentinel lymph node biopsy was performed in four cases, with no positive nodes. No adjuvant treatment was administered, as per multidisciplinary decision. After a median follow-up of 53 months, local recurrence (LR) occurred in 14 % of cases. Margin involvement strongly predicted LR, which was higher in patients with final positive margins (5/6, 83.3 % vs. 0/31, 0 % in patients with clear margins, p < 0.001). Conclusions: The 31.3 % upgrade ratio from pure P-/FLCIS to IC/DCIS recommends surgical excision. Axillary surgery should be omitted. Positive margins are strongly associated with LR. Surgery with negative margins is the mainstay of treatment. Larger multicentric studies are needed.