Tubal ligation exacerbates ovulation-driven TP53 mutagenesis and p53 signatures by depleting protective menstrual hemoglobin.

The fallopian tube epithelium (FTE) is the primary tissue of origin for ovarian high-grade serous carcinoma (HGSC), with ovulation implicated as a key risk factor. TP53 mutations, a hallmark of HGSC and its precursor lesions, such as p53 signature, are predominantly CG>TA substitutions attributed to cytidine deamination. We previously demonstrated that ovulatory follicular fluid (FF) released reactive oxygen species (ROS), which activate activation-induced cytidine deaminase (AID) and promote TP53 mutagenesis in FTE. Here, we demonstrate that hemoglobin (Hb) originating from retrograde menstruation acts as an extracellular ROS scavenger, attenuating AID-mediated TP53 deamination in fallopian tube fimbriae, both in vitro and in vivo. Peritoneal fluid from tubal-ligated women exhibited significantly lower Hb, higher ROS, and elevated hypoxanthine phosphoribosyl transferase (HPRT) mutagenic activity compared to nonligated controls (p < 0.004). Histopathological analysis of 206 fallopian tubes from 119 women undergoing opportunistic salpingectomy further revealed a significantly higher frequency of p53 signatures in ligated tubes (0.22 ± 0.64 lesions per fimbria) than in nonligated tubes (0.07 ± 0.31 lesions per fimbria) (p = 0.017). Multivariate analysis identified tubal ligation as the sole reproductive factor independently associated with p53 signatures [odds ratio (OR) = 3.32; 95% CI: 1.15-9.57]. Our findings indicate that retrograde menstrual Hb mitigates ovulation-associated ROS stress, thereby reducing AID-mediated TP53 mutagenesis in the FTE. This study uncovers a physiological, protective role for menstruation against ovulatory oxidative damage and its mutagenic consequences, while demonstrating that tubal ligation disrupts this endogenous antioxidant mechanism, resulting in an increased burden of p53 signature lesions. © 2026 The Pathological Society of Great Britain and Ireland.