Arsenic (a Group I carcinogen in humans) contamination and poisoning of human populations in different parts of Southeast and Eastern Asia, including West Bengal and Bangladesh, has become a major environmental concern. Arsenic intoxication affects diverse human organs including the lungs, liver, skin, bladder and kidney. This metalloid acts as a promoter of carcinogenesis, exerting toxic effects on the immune system. The present study was aimed at investigating arsenic-induced carcinogenesis and effects on the immune system in an animal model. Tumors were induced using ethylnitrosourea (ENU) and arsenic was used as a promoter. To investigate specific effects on the immune system, cytokine (TNF-α, IFNγ, IL4, IL6, IL10, IL12) production of lymphocytes was evaluated by FACS. The damaging consequences of treatment were assessed by evaluating the specific programmed cell death cascade in lymphocytes, assessed by FACS readings. The results revealed that under arsenic influence, and more so with arsenic+ENU, marked neoplastic changes were noted, which were corroborated with histological changes, cytokine modulation and apoptosis hinted at marked neoplastic changes.