Survival patterns of invasive lobular and invasive ductal breast cancer in a large population-based cohort with two decades of follow up.

Background: Invasive lobular carcinoma (ILC) comprises 8-15 % of all invasive breast cancers and large population-based studies with >10 years of follow-up are rare. Whether ILC has a long-time prognosis different from that of invasive ductal carcinoma, (IDC) remains controversial.

Purpose: To investigate the excess mortality rate ratio (EMRR) of patients with ILC and IDC and to correlate survival with clinical parameters in a large population-based cohort.

Material And Methods: From 1989 through 2006, we identified 17,481 patients diagnosed with IDC (n = 14,583) or ILC (n = 2898), younger than 76 years from two Swedish Regional Cancer Registries. Relative survival (RS) during 20 years of follow up was analysed.

Results: ILC was significantly associated with older age, larger tumours, ER positivity and well differentiated tumours. We noticed an improved survival for patients with ILC during the first five years, excess mortality rate ratio (EMRR) 0.64 (CI 95 % 0.53-0.77). This was shifted to a significant decreased survival 10-15 years after diagnosis (EMRR 1.49, CI 95 % 1.16-1.93). After 20 years the relative survival rates were similar, 0.72 for ILC and 0.73 for IDC.

Conclusions: During the first five years after surgery, the EMRR was lower for patients with ILC as compared to patients with IDC, but during the years 10-15 after surgery, we observed an increased EMRR for patients with ILC as compared to IDC. These EMRR between ILC and IDC were statistically significant but the absolute difference in excess mortality between the two groups was small.