Statistically significant decrease is observed at 7 weeks in females receiving 1.0 mg Benzo[a]pyrene (B[a]P) compare with the vehicle group. As lung tumorigenesis induced by Benzo[a]pyrene is dose dependent in female A/J mice. The incidence of hyperplasia values in females treating with 0.25, 0.50, and 1.0 mg Benzo[a]pyrene are significantly higher than in the vehicle-treated group. The incidence of adenoma in females receiving 1.0 mg Benzo[a]pyrene is significantly higher than in the vehicle group. The multiplicity of hyperplasia in females receiving 0.50 or 1.0 mg Benzo[a]pyrene is significantly higher than in the vehicle group. The multiplicity of adenoma in the group treated with 1.0 mg is also significantly higher than in the vehicle group. The incidences of hyperplasia and adenoma in female A/J mice are significantly increased by Benzo[a]pyrene in a dose-dependent manner. Benzo[a]pyrene induces an average of 9.38±1.75 tumors with an average tumor load of 19.53±3.81 mm ³ (P<0.05 compare to control). Benzo[a]pyrene administration significantly (P<0.05) decreases cAMP levels in tumors with adjacent lung tissues. The expression level of PDE4D gene is also increased by Benzo[a]pyrene administration.