Prognosis of rare histological subtypes of breast cancer : insights from the Bulgarian national cancer registry

Abstract

Background: Real world (RW) data obtained from population-based registries can provide precious information for rare cancers and can inspire strategies for improving outcomes. We aimed to investigate the tumor biology and outcomes of patients with rare histological subtypes of breast cancer (BC) registered in the Bulgarian National Cancer Registry (BNCR). Methods and materials: This is a retrospective study of patients diagnosed with rare histological types of BC and more than 100 registered cases in BNCR between 2012 and 2022: mucinous adenocarcinoma, medullary carcinoma, tubular and intraductal papillary carcinoma with invasion. We investigated the receptor status distribution and overall survival (OS) of the rare histological types and compared it with those of ductal cancer of no special type. Results: The majority of patients with the selected rare histological types were diagnosed in early stage. Progression to metastatic stage is observed most frequently in medullary carcinoma in up to 10,4 % of the cases. The 5-year observed OS was higher in patients with any of the rare subtypes compared to this in patients with ductal cancers. The best OS was observed among patients with intraductal papillary cancer with invasion, followed by the tubular histological type. Discussion: The good prognostic characteristics not always lead to an equally good treatment outcome. Histological classification of breast tumors is dynamic and further clarification of the prognostic impact of the different histological types is needed. Conclusion: Histological subtypes can define tumor behaviour and response to treatment and it should be taken into consideration in the decision-making process.