With largely improved cancer survivorship in past decades, cancer survivors developed second primary breast cancer (BCa-2) are not uncommon. However, little is known about the prognosis of BCa-2. We therefore aimed to examine the risk of breast cancer-specific mortality among patients with BCa-2 compared with those with first primary breast cancer (BCa-1).
We included all women diagnosed with invasive breast cancer from January 1, 1990 to December 31, 2015 in US who were recorded in the Surveillance, Epidemiology, and End Results (SEER) program. BCa-2 was defined in patients with a previous diagnosis of non-breast primary malignancy in SEER. We estimated the hazard ratios (HRs) of breast cancer-specific and overall mortality among patients with BCa-2 compared with BCa-1, using COX proportional hazard models adjusted for demographic, tumor, and clinical characteristics.
883,881 and 36,313 patients were identified as BCa-1 and BCa-2, respectively. The median intervals from first primary malignancy to BCa-2 diagnosis was 4.75 years. Compared to BCa-1, women with BCa-2 were diagnosed with less aggressive tumor and received less treatment. BCa-2 patients were associated with increased risks of breast cancer-specific mortality (HR: 1.12; 95% CI: 1.08-1.15) and overall mortality (HR: 1.57; 95% CI: 1.54-1.59). The risk increase was particularly greater when the first malignancy was at distant stage, severer in prognosis, diagnosed within 2 years, or treated by chemotherapy/ radiation therapy. Stronger associations were also found among women with HER2 (+), PR (-), ER (-), and those with less aggressive tumor features.
Patients with BCa-2 have worse breast cancer-specific survival and overall survival, compared with their BCa-1 counterparts. These findings emphasize the needs for more active treatment and surveillance for cancer survivors who developed BCa-2.
West China Hospital, Sichuan University.
National Natural Science Foundation of China (grant number: 81872307), Swedish Research Council (grant number: 2018-00648), and Science and Technology Foundation of Sichuan Province (grant number: 2017SZ0005).
All authors have declared no conflicts of interest.