Abstract P4-09-07: Higher risk of metachronous contralateral breast cancer in patients with invasive lobular breast cancer

Background: Risk of metachronous contralateral breast cancer (CBC) is an important health issue in primary breast cancer (PBC) survivors. Individualized CBC risk prediction can help identify patients at high or low risk who may or may not benefit from additional surveillance and treatment. For lobular PBC, inconsistent results have been reported on an association with increased risk of CBC. We investigated CBC risk in lobular versus ductal PBC using a large nationwide dataset and taking into account age at PBC and (neo-)adjuvant systemic therapy effects.

Patients and Methods: We selected women diagnosed between 2003 and 2010 with early invasive lobular, lobular mixed with other types, or ductal PBC from the Netherlands Cancer Registry. Categorical and continuous characteristics between the 3 groups were compared using the chi-square statistics and the Kruskal-Wallis test, respectively. Competing risk analyses were applied to determine CBC incidence. Multivariable subdistribution hazard ratios (SHRs) were adjusted for primary tumor stage, age at PBC diagnosis, radiotherapy, (neo-)adjuvant chemotherapy and endocrine therapy.

Results: We selected 74,373 women aged >18 years with lobular (n=8,903), lobular mixed (n=3,512), and ductal (n=62,230) PBC. Women with lobular PBC were older at diagnosis than women with lobular mixed or ductal PBC (61 vs. 58 vs. 58 years, respectively), more often had ER-positive PBC (95.7% vs. 94.1% vs. 79.6%) and were more often systemically treated with only endocrine therapy (30.7% vs. 24.9% vs. 19.7%), while less often treated with only chemotherapy (4.2% vs. 5.3% vs. 15.4%).

Ten-year cumulative CBC incidences in women with lobular, lobular mixed or ductal PBC were 3.2%, 3.6% and 2.8% when treated with systemic therapy (chemotherapy and/or endocrine therapy) and 6.6%, 7.7% and 5.6% without systemic therapy, respectively. Multivariable SHRs were 1.19 (95% CI: 1.05-1.34) for lobular and 1.39 (95% CI: 1.17-1.65) for lobular mixed versus ductal PBC; for women <50 years, risk differences were larger: 1.60 (95% CI: 1.26-2.05) and 1.43 (95% CI: 1.00-2.06), respectively.

Conclusion: Lobular histology and lobular mixed histology are independent risk factors for CBC development, and should be considered as prognostic factors when refining CBC risk prediction models.

Citation Format: Akdeniz D, Kramer I, van Deurzen CH, Schaapveld M, Westenend PJ, Voogd AC, Jager A, Steyerberg EW, Sleijfer S, Schmidt MK, Hooning MJ. Higher risk of metachronous contralateral breast cancer in patients with invasive lobular breast cancer [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P4-09-07.