Can Ki67 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 Ki67 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, and false-positive results in low-risk EBC with low and high Ki67 (</≥ 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. Also, rate of additional imaging or follow-up diagnostics due to suspicious findings was analyzed. The patients were divided into two groups (Ki67 < and ≥ 25%) and rates of distant metastases as well as 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 Ki67 < 25% and 46% (n = 87) having Ki67 ≥ 25%. Risk for distant metastases was 0% in Ki67 < 25% and 1.1% in patients with Ki67 ≥ 25% (p > 0,05, n.s.). Due to suspicious findings in the initial staging diagnostic, additional imaging was required for 11.8% (n = 12) of patients with Ki67 < 25% compared to 19.4% (n = 17) patients with Ki67 ≥ 25% resulting in a false positive rate of 11.8% (Ki67 < 25%) and 18.3% (Ki67 ≥ 25%), respectively. 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 Ki67 developed distant metastases. In these cases, staging diagnostics may be discussed with the patient.