Abstract PS14-09: The impact of non-classic LCIS on the natural history of DCIS

Background: Classic lobular carcinoma in situ (C-LCIS) and non-classic LCIS (NC-LCIS) are histologically and biologically distinct types of lobular neoplasia. Little is known about the impact of NC-LCIS on risk of recurrence when found in association with concomitant malignancy. We sought to assess oncologic outcomes in patients with DCIS and concomitant NC-LCIS as compared to DCIS with concomitant C-LCIS treated with breast conservation. Methods: Upon IRB approval, an institutional database was accessed to identify patients with a diagnosis of C-LCIS + DCIS or NC-LCIS+DCIS in the same core biopsy and/or excisional biopsy specimen. All pathology slides relevant to the diagnosis were confirmed by internal review. Patients with prior or concurrent ipsilateral invasive breast cancer and/or prior ipsilateral DCIS were excluded. Use of adjuvant therapies and the incidence of ipsilateral and contralateral DCIS and invasive breast cancer were compared in the 2 groups. Statistical analysis was performed using the chi-square test. Results: Among patients diagnosed with DCIS between 1996 and 2015 and treated with breast conserving surgery, 69 also had C-LCIS and 13 also had NC-LCIS (the diagnosis of NC-LCIS was not encountered until 2000). Median patient age was 55 years (range 40-88), 42 (51%) had a family history of breast cancer and 5 (6%) had a prior diagnosis of atypical proliferative breast lesions; these factors did not differ between patients with C-LCIS+DCIS and NC-LCIS+DCIS. Patients with NC-LCIS+DCIS were more likely to present with mammographic distortion (25% vs 6%, p=0.03), to have been diagnosed by core biopsy, and less likely to have ER positive (67% vs 91%, p=0.03) or PR positive (50% vs78%, p=0.014) DCIS. In 78% of the patient cohort, final excision margins were negative, and these proportions were not different between the 2 groups The median number of surgeries performed to obtain clear surgical margins which was 2 (range 1-4) for the entire cohort and for C-LCIS+DCIS and NC-LCIS+DCIS, individually. 78.% of C-LCIS+DCIS patients and 54% of NC-LCIS+DCIS patients received adjuvant radiation (p=0.064), and 45% of C-LCIS+DCIS patients took adjuvant hormonal therapy, while none of the NC-LCIS+DCIS patients did (p=0.002). At median follow-up of 78 (1-260) months for C-LCIS+DCIS and 60 (1-197) months for NC-LCIS+DCIS, there were no differences observed in the incidence of ipsilateral and contralateral breast cancer (10.1% vs 7.7% , p=0.19, and 10.1% vs 0%, respectively, p=0.78). One of 13 patients (7.7%) with NC-LCIS+DCIS, who developed an ipsilateral invasive carcinoma, was subsequently diagnosed with bone metastasis. Conclusions: Patients with NC-LCIS+DCIS were more likely to have ER and/or PR negative DCIS and only 54% of this cohort received radiation, yet local-regional recurrence rates were low and not different between NC-LCIS +DCIS and C-LCIS+DCIS patients. Despite the more aggressive histologic features of NC-LCIS, these data do not suggest that NC-LCIS associated with DCIS portends a different prognosis that C-LCIS associated with DCIS. Larger studies are needed to confirm these findings. Citation Format: Faina Nakhlis, Fisher Katlin, Samantha Grossmith, Ashley DiPasquale, Beth Harrison, Tari King. The impact of non-classic LCIS on the natural history of DCIS [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS14-09.