Pregnancy occurring during or following adjuvant trastuzumab in patients enrolled in the HERA trial (BIG 01-01)

Only few case reports describe the pregnancy course and outcome of breast cancer patients, who were under treatment with trastuzumab at the time of conception or who have completed trastuzumab therapy before becoming pregnant. The HERA trial is a large phase III randomized clinical trial in which patients with early HER2-positive breast cancer were randomized to receive 1 or 2 years of trastuzumab or observation following completion of primary chemotherapy. To examine the effect of trastuzumab on pregnancy outcome, we report all pregnancy events that occurred until March 2010 in patients enrolled in the study. For the sake of this analysis, patients were assigned to three groups: (1) pregnancy occurring during and up to 3 months after trastuzumab exposure (group 1); (2) pregnancy occurring >3 months of last trastuzumab dose (group 2); and (3) pregnancy occurring in patients without prior exposure to trastuzumab (group 3). Sixteen, 45 and 9 pregnancies took place in groups 1, 2, and 3, respectively. 25 and 16% of patients in groups 1 and 2 experienced spontaneous abortion, the former being higher than figures reported in the general population. However, short-term fetal outcome appeared normal across the three groups. Only 2 congenital anomalies were reported, one in group 2 and one in group 3. No congenital anomalies were reported in those exposed to trastuzumab in utero. This is the first report from a large randomized trial assessing the effect of trastuzumab on pregnancy course and outcome. Based on our results, trastuzumab does not appear to affect fetal outcome in patients who manage to complete their pregnancy. We are currently initiating a collaboration to collect similar data from the other large adjuvant trastuzumab trials to confirm these findings.