High Ki67 predicts unfavourable outcomes in early breast cancer patients with a clinically clear axilla who do not receive axillary dissection or axillary radiotherapy.

Aim: Axillary dissection is increasingly forgone in early breast cancer patients with a clinically negative axilla. The GRISO 053 randomised trial recruited 435 patients of age over 45 years, tumour ≤1.4 cm and clinically negative axilla, to assess the importance of axillary radiotherapy versus no axillary radiotherapy in patients not given axillary dissection. In the present study on a subgroup GRISO cases our aim was to assess the prognostic importance of tumour biological factors after more than 10 years of follow-up.

Methods: We retrospectively assessed biological factors in a subgroup of 285 GRISO cases (145 given axillary radiotherapy; 140 not given axillary radiotherapy) with complete biologic, therapeutic and follow-up information, using multivariable Cox proportional hazards regression modelling.

Results: Only 10-year cumulative incidence of distant metastasis was lower in the axillary radiotherapy (1%) than no axillary radiotherapy arm (7%) (p=0.037). Irrespective of study arm, hormone receptor positivity had significantly favourable effects on 10-year disease-free survival (DFS) and overall survival. human epidermal growth factor receptor 2 (HER2)-positive and triple-negative subtypes were associated with lower 10-year DFS (60% and 76%, respectively) than luminal A (96%) and B (91%) (p=0.001). Ten-year DFS for high (≥14%) Ki67 cancers was lower than for low Ki67 cancers (p=0.027); however, this effect was mainly confined to the no axillary radiotherapy arm.

Concluding Statement: For patients with clinically node-negative small breast cancer not given axillary dissection, 10-year DFS is worsened by HER2 positivity, triple-negative phenotype and high Ki67. Axillary radiotherapy counteracts the negative prognostic effect of high Ki67 in patients not receiving axillary dissection.