Invasive lobular breast cancer in young patients without adjuvant systemic treatment: 15-year survival outcomes

Invasive lobular carcinoma (ILC) of the breast typically affects older women. As a result, there is limited research on prognosis and prognostic factors in young women with ILC. Here we set out to determine the long-term outcome and prognostic factors of women under 40 years of age with lymph node-negative (N0), hormone-receptor positive (HR+)/human epidermal growth-factor receptor 2 negative (HER2-) ILC who did not receive adjuvant systemic treatment (chemo- and/or endocrine therapy).

Through the Netherlands Cancer Registry we selected all systemically untreated patients younger than 40 years with HR+/HER2-, N0, early breast cancer diagnosed in the Netherlands from 1989-2000. At the time, node-negativity was considered a favorable prognostic marker and guidelines recommended no adjuvant systemic therapy for this subgroup. Distant recurrence-free survival (DRFS), recurrence-free survival (RFS) and overall survival (OS) were assessed according to the STEEP criteria. Uni- and multivariable Cox proportional hazard models were used to assess prognosis, calculating hazard ratios (HR) with confidence interval (CI).

Of the n = 1138 selected patients, n = 95 were histologically classified as ILC and n = 805 as invasive breast cancer of no special type (BC-NST), n = 238 were classified as other breast cancer subtype. In ILC, tumor grade was not associated with DRFS/RFS or OS (HR for DRFS 1.40, 95%CI 0.42-4.63). However, the presence of lymphovascular invasion (LVI) (adjusted HR DRFS 2.81, 95%CI 1.14-6.94, p < 0.05) and multifocality (adjusted HR DRFS 3.28, 95%CI 1.49-7.22, p < 0.01) were. When comparing DRFS, RFS and OS in matched low-risk luminal A-like ILC vs. BC-NST, we observed a trend for worse 15-year survival in ILC (15-year DRFS 63% in ILC vs. 74% in BC-NST; HR 1.50, 95%CI 0.98-2.29, p = 0.06).

In these young patients with systemically untreated N0 ILC we show that grade was not prognostic at 15 years follow-up, whereas LVI and multifocality were. Furthermore, ILC had a numerically worse 15-year survival than matched luminal A-like BC-NST.