Long-term outcomes of rare pure histological subtypes of breast cancer in a tertiary single-center retrospective cohort

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BACKGROUND: Rare pure histological breast cancer subtypes represent a clinically heterogeneous group of tumors with diverse biological behaviours and prognostic profiles. Due to their rarity, data, particularly regarding long-term survival outcomes, are limited and controversial. This study aimed to evaluate the clinicopathological features and long-term survival outcomes of patients diagnosed with rare pure histological breast cancer subtypes in a single tertiary center. METHODS: This retrospective single-center study included 117 patients diagnosed with pure rare breast cancer histologies between November 2000 and February 2024. These included mucinous, metaplastic, micropapillary, and tubular carcinomas, as well as malignant phyllodes tumors. Clinicopathological features, treatment methods, recurrence risks, and survival outcomes were analyzed. 5-year and 10-year overall survival (OS) rates were calculated. RESULTS: The most common subtype was mucinous carcinoma (41.9%), followed by metaplastic (25.6%), micropapillary (14.5%), tubular carcinoma (10.2%), and malignant phyllodes tumor (7.7%). Favourable biological features such as low grade, low Ki-67 proliferation index, and high hormone receptor expression were dominant in mucinous and tubular carcinomas, while metaplastic and micropapillary carcinomas frequently exhibited aggressive biological features such as high grade, high Ki-67, and more frequent lymph node involvement. In long-term follow-up, recurrence was most common in malignant phyllodes tumors, micropapillary carcinomas, and metaplastic carcinomas. Five- and ten-year overall survival rates differed significantly among subtypes, with the most favourable outcomes observed in tubular and mucinous carcinomas and relatively lower long-term survival observed in metaplastic and malignant phyllodes tumors. CONCLUSIONS: Pure rare histological breast cancer subtypes appear to show heterogeneity in clinicopathological features and long-term survival outcomes. Due to the small number of patients in individual subgroups, these findings should be interpreted with caution. Our descriptive data suggest a potential prognostic role for histological subtype and highlight the importance of accurate pathological classification. Long-term follow-up data from tertiary care centers may provide useful descriptive information about the natural history and survival patterns of these rare breast cancer subtypes.

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