Association of drainage volume decline trajectories during the first 7 postoperative days with persistent seroma on postoperative day 30 after modified radical mastectomy for breast cancer

Background Persistent seroma after modified radical mastectomy (MRM) with axillary lymph node dissection (ALND) can prolong drainage and recovery. We identified drainage trajectories during the first postoperative week and evaluated their association with persistent seroma on postoperative day 30. Methods This single-center retrospective study included 306 adults with unilateral invasive breast cancer who underwent MRM with level I–II ALND between 2021 and 2024. Trajectories of daily combined drainage volume were identified using latent class mixed-effects models. Firth penalized-likelihood logistic regression was used to adjust for age, body mass index, diabetes mellitus, neoadjuvant systemic therapy, resected specimen weight, operative time, and the number of dissected lymph nodes. Sensitivity analyses addressed uncertainty in class assignment, outcome definition, retention of the original drain, pathologic T category, and operating surgeon. Exploratory complete-case models compared trajectory classification with simpler drainage measures. Results Rapid-decline (123 patients), moderate-decline (127 patients), and persistently high-output (56 patients) trajectories were identified. Persistent seroma occurred in 7.3%, 19.7%, and 57.1% of patients, respectively ( P < 0.001). Relative to the rapid-decline trajectory, the adjusted odds ratios were 2.58 [95% confidence interval (CI), 1.10–6.07] and 11.44 (95% CI, 3.92–33.37), respectively. The association for the persistently high-output trajectory remained strong across sensitivity analyses, whereas that for the moderate-decline trajectory was less stable. The trajectory and postoperative day 7 (D7) drainage models showed similar discrimination. Adding trajectory class provided little incremental information beyond D7 drainage but improved model fit and discrimination beyond 7-day cumulative drainage and the relative decline from postoperative day 1 (D1) to D7. Conclusions Persistently high output was consistently associated with persistent seroma on postoperative day 30. Trajectory classification should remain a research-oriented postoperative risk-stratification variable. The incremental clinical value of trajectory classification over the simpler D7 drainage measurement remains uncertain and requires prospective validation. Clinical application requires multicenter external validation, assessment of class-assignment reproducibility, calibration, clinically meaningful thresholds, and evaluation of clinical utility.