The possible protective effect of Piper aduncum capsule on DMBA (dimethylbenz[α]anthracene)-induced breast cancer in rats was assessed by monitoring the tumor and lung metastases incidence and recording hematological and biochemical parameters and frequency of micronuclei. Mammary carcinogenesis was induced in 36 female Holtzman rats by providing a single subcutaneous injection of DMBA. Oral administration of P. aduncum capsule lowered adenocarcinoma and lymph node metastases incidence. Pulmonary metastasis was significantly lowered (P < 0.05). Hematological indicators showed that the triglyceride level was significantly lowered (P < 0.01) and high-density lipoprotein (HDL) level was significantly increased (P < 0.01). Also, P. aduncum capsule significantly lowered the C reactive protein (CRP) level (P < 0.01) and malondialdehyde level (P < 0.05). There was a significant decrease in the frequency of DMBA-induced micronucleated polychromatic erythrocyte (P < 0.01). Considering the antitumorigenic, hypolipidemic, anti-inflammatory, antioxidant, and antigenotoxic properties of P. aduncum capsule, we conclude that it has a protective effect on DMBA-induced breast cancer in rats.