Surgical bleeding complications typically occur a few hours or days after the operation. Due to their rarity, late-onset bleeding complications are seldom discussed in the literature. Mastectomy is a common procedure, which is often associated with the need for repeated seroma aspirations. Although seroma aspirations have also been associated with complications, the area remains insufficiently studied. This study aimed to investigate the risk of late bleeding complications after mastectomy, especially those associated with seroma aspiration.

Data from all patients undergoing simple mastectomy with or without axillary surgery for breast cancer between 2010 and 2022 at a single university hospital were collected. Medical records were reviewed for major bleeding complications and predisposing factors, especially the use of antithrombotic medications.

In total, 2,620 patients with 2,710 mastectomies were included in the study. Forty-five patients (1.7%) suffered a major bleeding complication. Twenty-four complications (53%) occurred after the first postoperative week; most (88%, 21/24) being preceded by a seroma aspiration. The median time from mastectomy to seroma aspiration-associated bleeding complication was 76 days (range 11–536 days). Upon arrival for treatment, 691 (26%) patients were taking antithrombotic medications. The risk for major bleeding complications related to seroma aspiration was 1.9% (13/691) and 0.4% (8/1929) in patients receiving and not receiving antithrombotic medications, respectively (p < 0.0001).

A significant proportion of major post-mastectomy bleeding complications occur late and are associated with seroma aspiration, particularly in patients receiving antithrombotic therapy. The indication, technique, and setting of seroma aspiration in these high-risk patients should be carefully considered.