Abstract P4-02-25: Analysis of prognosis in different subtypes of invasive lobular carcinoma using a National Cancer Database Breast Cancer Registry of Japan
Authors: Adachi Yayoi , Asaga Sota , Kumamaru Hiraku , Yamamoto Yutaka , Imoto Shigeru , Jinno Hiromitsu 
Published: March 2023

Abstract
[Introduction] Invasive lobular carcinoma (ILC) has different pathological and clinical features from invasive ductal carcinoma (IDC). ILC has more likely to be hormone receptor (HR) positive, and several studies reported that the prognosis of ILC was better than IDC. However, ILC also has different prognosis according to the subtypes as IDC does, and better prognosis of ILC might depend on their high HR positivity. Additionally, there are many reports that chemotherapy (CT) does not improve the prognosis of ILC due to the high positivity of HR. Therefore, we compared the prognosis of ILC and IDC in the same subtypes and considered necessity of CT for luminal ILC. ILC usually constitutes small population of invasive breast cancer. Thus, we have planed the analysis by using the Breast Cancer Registry (BCR) run on the National Cancer Database (NCD) in Japan. [Methods] 318,338 breast cancer patients were registered in BCR between 2004 and 2012. We selected 250,736 patients who were diagnosed as ILC or IDC. Patients with distant metastasis, those who did not receive surgery, and those who received preoperative therapy, and those who had bilateral breast cancer were excluded, and it resulted in 207,428 patients. Of these cases, the cases with 10-year follow-up data were 136,654, and we examined 5,705 ILC and 130,949, IDC. Because it was presumed that there are differences in pathological and clinical characteristics between ILC and IDC, we have planned to make the matched cohorts by using exact matching for comparing their prognosis. To evaluate the prognosis of each subtype, we compared DFS and OS for IDC and ILC in each subtype. To evaluate the effect of CT in luminal ILC, we corrected the data of luminal ILC with pT2N0M0 or pT1-2N1M0 patients and compared DFS and OS between endocrine therapy (ET) only group and ET+CT group. DFS was defined as the time from surgery to local or distant recurrence or death from any cause. OS was defined as the time between the surgery and the death from any cause. Peason’s Chi squared test was used to identify the characteristics. Survival curves were constructed by Kaplan-Meier method and were compared by log-rank test. [Results] We made the matched cohort by using exact matching and we identified 5,633 ILC and 5,633 IDC for prognosis analysis. In overall subtypes, the 10-year DFS of ILC was poor than those of IDC (76.56% vs 79.14%, p=0.04). In the analysis by each subtype, there was no statistical difference in DFS for luminal HER2, HER2, and TN cohorts, however luminal ILC had statistically significant poor DFS than luminal IDC (78.04% vs 81.17%, p&lt; 0.01). The analysis of 10-year OS showed similar results, and there were no differences in the OS of luminal HER2, HER2 and TN cohorts between ILC and IDC. However, ILC had worse OS than IDC in luminal cohort (85.95% vs 89.13%, p&lt; 0.01). To evaluate the effect of CT in luminal ILC, we made the matched cohort and we identified 95 luminal IDC and 95 luminal ILC in pT2N0 cohort, and 83 luminal IDC and 83 luminal ILC in pT1-2N1 cohort for the analysis. In pT2N0 cohort, the 10-year DFS was 82.12% in ET+CT group and 87.35% in ET only group (p=0.99). The OS of the ET+CT and the ET only group was 93.48% and 94.04% (p=0.88). In pT1-2N1 cohort, the ET only group had 54.17% and the ET+CT group had 77.03% of DFS (p=0.34). The OS in the ET only group and the ET+CT group was 61.96% and 94.81% (p=0.01). [Discussion] Although luminal HER2, HER2 and TN cohorts had no differences in prognosis between ILC and IDC, luminal ILC had a poor prognosis than luminal IDC. Therefore, luminal ILC needs stronger approach to improve their prognosis. And it was suggested that chemotherapy is effective for recurrent high-risk luminal ILC such as those with positive lymph node metastasis. [Conclusion] ILC had worse prognosis than IDC in luminal cohort, however it was comparable in luminal HER2, HER2, TN cohorts. A new strategy of treatments for luminal ILC might be needed to improve their prognosis.
Citation Format: Yayoi Adachi, Sota Asaga, Hiraku Kumamaru, Yutaka Yamamoto, Shigeru Imoto, Hiromitsu Jinno. Analysis of prognosis in different subtypes of invasive lobular carcinoma using a National Cancer Database Breast Cancer Registry of Japan [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P4-02-25.