We assayed for the presence of human papilloma virus (HPV) DNA in serum and͞or peripheral blood fraction (PBF) of individuals with cervical, head͞neck, or bladder cancer due to schistosomiasis. Using mass spectroscopy coupled with competitive PCR, HPV DNA was detected at the individual molecule level by using ''Mass-ARRAY'' assays. The resultant sensitivity was superior to real-time fluorescent PCR-based assays, while specificity was maintained. Our principal findings were: (i) Virtually all tested cervical cancers and schistosomiasis-associated bladder cancers, and a plurality of head͞neck cancers, are associated with HPV DNA in the tumor. (ii) All 27 bladder cancers due to schistosomiasis were associated with the presence of HPV-16 DNA, which can be detected in tumor and serum but not in PBF. In contrast, no serum HPV-16 DNA signal was detected in seven individuals with schistosomiasis-associated bladder cancers after surgical removal of the tumor. cancer diagnosis ͉ cancer treatment ͉ bilharziasis R ecent studies indicate that the human papillomavirus (HPV) is associated with a significant fraction of cervical (1, 2), head͞neck (3), and schistosomiasis-associated bladder cancers (4). Cervical cancers are almost uniformly associated with HPV infection (5). In a review of published reports, McKaig et al. (3) found the overall prevalence of HPV DNA in head and neck tumors to be 35%. More recently, Gillison et al. (6) used quantitative PCR (QPCR) to confirm these findings in a large study of 253 tumor samples. They detected HPV DNA in 25% of specimens. Khaled et al. (4) found that nearly 50% of schistosomiasis-caused bladder cancers had HPV DNA by in situ hybridization. This body of work argues that HPV could be a useful tag for tracking a considerable fraction of cervical, head͞neck, and schistosomiasis-associated bladder cancers.HPV types 16 and 18 are among the ''high-risk'' viral types, because their presence is associated with preneoplastic lesions and carcinomas. In contrast, the ''low-risk'' types, most commonly types 6 and 11, are typically associated with benign lesions. The oncogenic potential of HPV is principally due to two viral oncoproteins, E6 and E7. Differences in oncogenic potential among HPV types have been attributed to type-specific differences in the E6 and E7 proteins (7). The E6 protein of oncogenic HPV strains has been shown to interact with the p53 protein and promote its degradation via a ubiquitin-dependent pathway (7). The E7 oncoprotein, similarly, can complex with the retinoblastoma (Rb) protein and inactivate it (8). Both p53 and Rb are important tumor suppressor genes whose products regulate the cell cycle, orchestrate DNA repair processes, and are involved with programmed cell death or apoptosis. Disruption of these tumor suppressor proteins by HPV leads to propagation of mutational changes and cell immortalization.Since the work of Anker, Sidransky, and coworkers (9-11) established that abnormal genomic DNA can be detected in serum of cancer patients, the technique of examin...