Differences in clinicopathologic features and subtype distribution of invasive breast cancer between women older and younger than 40 years

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Objectives: We investigated and compared clinicopathologic features and subtype distribution of invasive breast cancer among women <40 and ≥40 years of age.

Methods: We retrospectively compared clinicopathologic characteristics and subtype distribution of invasive breast cancer in women <40 and ≥40 years of age, in a cohort of 1,130 patients. Subtypes included luminal A (positive for hormone receptors [HR]—estrogen receptor [ER] and/or progesterone receptor [PR]—and negative for human epidermal growth factor receptor 2 [HER2] with low Ki67), luminal B (HER2^–) (HR⁺/HER2^–/Ki67^High), luminal B (HER2⁺) (HR⁺/HER2⁺), HER2-overexpressing (HR^–/HER2⁺), and triple negative (ER^–/PR^–/HER2^–).

Results: Breast cancers in younger women had unfavorable clinicopathologic characteristics, including larger tumors and more frequent node involvement. Subtypes among the 1,130 tumors were luminal A: 36.4%, luminal B (HER2^–): 35.0%, luminal B (HER2⁺): 7.5%, HER2-overexpressing: 7.1%, and triple negative: 14.0%. The age groups significantly differed in subtype distribution (P<0.001). Luminal A subtype was more common in the older group (38.5%) than the younger group (16.2%), and luminal B (HER2^–) was more common in the younger group (52.2%) than in the older group (33.2%; P<0.001).

Conclusions: Breast cancers in women younger than 40 years have unfavorable clinicopathologic characteristics and are more likely to be luminal B (HER2^–) and less likely to be luminal A than breast cancers in older women.