Elevated levels of serum immunoglobulin observed in patients with cancers of epithelial origin, including carcinomas of breast, colon, and liver 1,2have been interpreted as humoral responses of host to cancer growth.3 Recently, Qiu et al4 described in detail that human cancers of epithelial origin, including carcinomas of breast, colon, liver, lung, established epithelial cancer lines, produce immunoglobulin G (IgG) in their cytoplasm. Under normal conditions, heat shock proteins (HSPs) have multiple cellular functions, such as folding and translocating newly synthesized proteins. When a cell is injured or under stress, HSPs refold damaged protein or facilitate degradation of proteins. In most cancers, heat shock proteins can capture tumour specific peptide to inhibit the growth of cancer. This study demonstrated that human IgG and HSPs are co-localized in hepatocellular carcinoma.Department of Pathology, State Key Laboratory of Cancer Biology, Xijing Hospital, Fourth Military Medical University, Xi’an 710032, China (Duan CG, Liu YF, Li KN, Yu L, Cui JH, Li J and Yang SJ) Elevated levels of serum immunoglobulin observed in patients with cancers of epithelial origin, including carcinomas of breast, colon, and liver 1,2 have been interpreted as humoral responses of host to cancer growth. 3 Recently, Qiu et al 4 in detail that human cancers of epithelial origin, including carcinomas of breast, colon, liver, lung, established epithelial cancer lines, produce immunoglobulin G (IgG) in their cytoplasm. Under normal conditions, heat shock proteins (HSPs) have multiple cellular functions, such as folding and translocating newly synthesized proteins. When a cell is injured or under stress, HSPs refold damaged protein or facilitate degradation of proteins. In most cancers, heat shock proteins can capture tumor specific peptides to inhibit the growth of cancer. This study demonstrated that human IgG and HSPs are co-localized in hepatocellular carcinoma. Department of Pathology, State Key Laboratory of Cancer Biology, Xijing Hospital, Fourth Military Medical University, Xi’an 710032, China (Duan CG, Liu YF, Li KN, Yu L, Cui JH, Li J and Yang SJ)