Does pregnancy impact on breast cancer treatment and outcomes? Case study in the East coast of Spain

Abstract Background A worse prognosis has been reported for breast cancer (BC) occurring some years after pregnancy. The study aim was to explore the potential differences in BC stage, treatment and survival between women with and without pregnancy during the period 2009-2019 before BC diagnosis Methods Women between 15-55 year old residents in Castelló (Spain) diagnosed of BC in 2019 were obtained from the Castelló population-based cancer registry. Previous pregnancies between 2009 and 2019 were identified from the Birth Registry or perinatal Mortality Registry. BC stage and treatment type in women with previous pregnancy (P) were compared with those in women without pregnancy (No-P). Fisher's exact test was used for comparing categorical variables (stage and treatment). 5 years observed and relative survivals and their 95% confidence intervals (CI) were estimated using the WAERS tool Results A total of 146 BC cases were obtained (33 with previous pregnancy). Stage II was the most frequent (55%) in P women and stage I (51%) in No-P (p < 0.05). The most frequent first course of treatment scheme for stage I and stage II in P women was Surgery (S)/Chemotherapy/Hormone therapy (HT)/Radiotherapy (RT) and in No-P was S/HT/RT but non-significant differences were found. The first course of treatment was given in the first year after diagnosis, with non-significant differences between P and No-P women. Relative 5-year survival in P women was 91.1% (95%CI: 81.8-100.2) and in No-P 95.4% (95%CI: 91.3-99.7). Non statistical significant differences in survival were found by stage between groups Conclusions Significant differences in BC stage were found in P women compared with No-P. 5-year survival was lower in P women, but non-significant differences were found. The main limitation was the low number of cases. A further study is planed extending the study period. A collaborative European project would increase the statistical power Key messages • The results suggested that women with previous pregnancies had more frequently a BC stage more advanced (stage II) than those without (stage I). No significant differences in survival were found. • No significant differences were found in either treatment scheme or time between diagnosis and treatment in women with BC whether they have previous pregnancies or not.