Spontaneous tumors in long-term--vasectomized mice. Increased incidence and association with antisperm immunity.

In two independent studies the authors have observed a significantly higher incidence of spontaneous tumors in vasectomized BDF1 mice over the long term than in age-matched sham-vasectomized control mice. In the first study, necropsies were performed on the animals at 30 months of age (27 months after surgery), and 15 of 24 vasectomized versus 2 of 14 sham-vasectomized mice (P less than or equal to 0.025) had detectable tumors in various tissues. In a second study, necropsies were performed on the animals at a younger age (18 months, 15 months after surgery), and liver tumors predominated: 82 of 171 vasectomized versus 33 of 97 controls (48% versus 34%, P less than or equal to 0.037) had at least one hepatic tumor, and a significantly higher percentage of vasectomized animals had large (greater than or equal to 31 sq mm) hepatic tumor burdens (80% versus 49%; P less than or equal to 0.002) and multiple hepatic tumors (19% versus 5%; P less than or equal to 0.002). In combined data from both studies, the vasectomy group had a higher incidence of (1) at least one tumor (P less than or equal to 0.025), (2) multiple tumors (P less than or equal to 0.005), and (3) more than one type of tumor (P less than or equal to 0.05. Furthermore, in both studies tumor number and size were significantly associated with antisperm immunity detected by antibody or aspermatogenesis evaluation. It is speculated that sperm degradation products and/or the autoimmune response to sperm that commonly accompanies vasectomy may affect tumor induction or growth directly or indirectly by interfering with immunosurveillance mechanisms.