| Summary: | Introduction: The prevalence of pregnancy-associated breast cancer is increasing. HER2-positive breast cancers typically have a poor prognosis. The objective of our study was to compare the prognosis of patients with HER2-positive breast cancer diagnosed during pregnancy (HER2-positive BCP) to young women diagnosed with HER2-positive breast cancer outside of pregnancy (HER2 non-BCP). Methods: Data of patients managed for invasive breast carcinoma between January 2005 and 2020 were retrospectively collected from the database of Tenon University Hospital (Paris, France), part of the “Cancer lié à la Grossesse” network. Results: Fifty-one patients with HER2-positive BCP were matched on age at diagnosis with 51 HER2-positive non-BCP patients. Locally advanced disease with axillary lymph node involvement were frequent. Tumors were frequently aggressive with high grade (p = 0.57) and high Ki67 (p = 0.15). Among the HER2-positive BCP patients, the mean term at diagnosis was 19.3 week of gestation (WG). Eighty-four percent of the patients continued their pregnancy with a mean term at delivery of 34.2WG. Chemotherapy modalities differed between the two groups: neoadjuvant chemotherapy was more frequent in the HER2-positive BCP group (p = 0.03) and adjuvant chemotherapy more frequent in the HER2 non-BCP group (p = 0.009). The recurrence rate was 10% (n = 5) and 18% (n = 9) in the HER2-positive BCP and HER2 non-BCP groups, respectively, p = 0.25. Breast cancer-free survival was poorer in the HER2-positive BCP group with earlier recurrence, p = 0.008. No difference in type of recurrence was found between the groups (p = 0.58). Conclusion: This matched case-control study implies that patients with HER2-positive BCP still have a poorer prognosis than non-pregnant HER-positive patients.
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