# Multicenter Assessment of Postoperative Mastocheck® Dynamics Following Curative Breast Cancer Surgery

## TL;DR

This study confirms that Mastocheck® values decrease consistently after breast cancer surgery across two different groups, supporting its use as a blood-based indicator for postoperative recovery.

## Contribution

The study demonstrates reproducible postoperative Mastocheck® dynamics across two independent clinical cohorts with different assessment designs.

## Key findings

- Mastocheck® values significantly decreased postoperatively in both cohorts.
- Most patients transitioned from above to below the diagnostic cut-off after surgery.
- Longitudinal follow-up showed sustained decline in Mastocheck® values over time.

## Abstract

These reproducible postoperative changes support Mastocheck® as a complementary blood-based readout for characterizing postoperative decline dynamics and contextualizing follow-up measurements. In this study, consistent decreases in Mastocheck® values were observed across two independent cohorts with different postoperative assessment designs, along with transitions from above to below the predefined diagnostic cut-off after surgery. These findings indicate stable normalization of tumor-associated signals over time and provide a useful framework for interpreting longitudinal measurements during follow-up. However, surveillance performance for recurrence detection was not evaluated and requires validation in future outcome-adjudicated prospective studies.

Purpose: Previous single-institution studies reported postoperative decreases in Mastocheck® values following breast cancer surgery. This study aimed to assess the reproducibility of these postoperative changes using two independent clinical cohorts with distinct postoperative assessment designs. Methods: Postoperative Mastocheck® dynamics were evaluated in two independent cohorts with distinct postoperative assessment designs. In the CHA Gangnam Medical Center (CHA University/CHA Medical Center, Seoul, Republic of Korea) cohort, Mastocheck® values obtained before surgery were compared with postoperative values preoperative values (n = 210) were compared with an independent postoperative set obtained ≥6 months after surgery (n = 171; median 378 days), and a paired subset (n = 28) was analyzed for within-patient changes. In an independent cohort from Myongji Hospital, only postoperative patients were enrolled, and longitudinal Mastocheck® measurements were analyzed in patients with four consecutive postoperative assessments. Changes in Mastocheck® values and transitions across the predefined diagnostic cut-off (0.0668) were evaluated. Results: In the CHA cohort, Mastocheck® values were significantly lower in the postoperative set than in the preoperative set (p < 0.001). Within the paired subset, among patients above the cut-off preoperatively (n = 20), 90.0% (18/20) converted to below the cut-off postoperatively, and paired analysis confirmed a significant postoperative decrease (Wilcoxon signed-rank test, two-tailed, p = 1.72 × 10−4). In the Myongji cohort, longitudinal follow-up demonstrated a sustained decline in Mastocheck® values over time, accompanied by a stepwise reduction in the proportion of patients exceeding the cut-off, reaching 0% at the final follow-up. Conclusions: Across two independent cohorts with complementary postoperative assessment strategies, Mastocheck® values consistently decreased after breast cancer surgery and shifted to, or were maintained below, the predefined diagnostic cut-off. These findings reproduce and extend prior single-institution observations, supporting the reproducibility of Mastocheck® postoperative decline dynamics and cut-off transitions across independent cohorts. This study did not evaluate recurrence detection, imaging concordance, or survival outcomes, and therefore does not establish clinical surveillance performance.