Can Ki-67 serve as a suitable marker to indicate the necessity of staging diagnostics in cases of low-risk breast cancer?

Background: For many years, staging tests have not been routinely employed for low-risk early breast cancer (EBC). However, the role of Ki-67 in determining the need for staging tests in low-risk EBC remains unclear. Our study aimed to assess the number and types of staging diagnostics, additional imaging, false-positive results, and rate of distant metastases in low-risk EBC with low and high Ki-67 (< / ≥ 25%).

Methods: This is a retrospective, single institution cohort study. All patients with newly diagnosed low-risk breast cancer at the University Medical Center in Freiburg in 2017 and 2021 were included. Low-risk was defined as clinical tumor stage T1/2, node negative (N0), hormone receptor positive, HER2 negative, asymptomatic EBC. Information on demographics, clinical and pathological characteristics, as well as number and type of performed staging diagnostics was obtained. Rate and type of additional imaging or follow-up diagnostics due to suspicious findings was analyzed. The patients were divided into two groups (Ki-67 < and ≥ 25%) and rates of distant metastases, performed staging diagnostics and false positive rates were compared.

Results: A total of 189 patients with low-risk EBC were identified, with 54% (n = 102) having Ki-67 < 25% and 46% (n = 87) having Ki-67 ≥ 25%. Risk for distant metastases was 0% in Ki-67 < 25% and 1.1% in patients with Ki-67 ≥ 25% (p = 0.46). Due to suspicious findings in the initial staging diagnostic, additional imaging was required for 11.8% (n = 12) of patients with Ki-67 < 25% compared to 19.5% (n = 17) of patients with Ki-67 ≥ 25% (p = 0.16). False positive rates did not differ significantly between the two groups (7.6% in Ki-67 < 25% vs. 9.8% in Ki-67 ≥ 25%; p = 0.55).

Conclusion: Distant metastases are rare in low-risk EBC. All in all, staging diagnostics should not be routinely employed in this patient population. Only patients with high Ki-67 developed distant metastases. In these cases, staging diagnostics may be discussed with the patient.