The expression of BCL2, BAX, and Caspase-3 in the tumor samples (the treated mice with 0.25 mg/kg SWCNT, 0.5 mg/kg MWCNT, and 2.5 mg/kg Doxorubicin) compared to the control was as follow: the expression of BCL2 in the tumor treated with MWCNT was significantly decreased in comparison with the control group (p < 0.05). The gene discussed is BCL2; the disease is neoplasm.