We have developed 2 new quantitative methods for measuring anti-p53 antibodies in human serum. Using these methods we analyzed 1,392 sera from patients with various malignancies and 230 sera from individuals without malignancy. Highest prevalence of anti-p53 antibodies was associated with ovarian and colon cancers (15%), followed by lung (8%) and breast (5%) cancers. Prevalence in other malignancies was lower (< 4%). In hospitalized patients and apparently healthy individuals, prevalence was very low (< 2 and 1% respectively). Extremely high antibody concentrations (> 10(5) U/L) were found in 5 ovarian, 2 breast, 1 lung and 1 colon cancers. Sequential analysis of 6 positive samples has shown that the p53 antibody test may have potential for patient monitoring. The p53 antibody-positive sera from breast cancer patients were associated with tumors that were steroid hormone receptor-negative (p < 0.002). We propose that the measurement of p53 antibodies is a relatively specific serological test for cancer, which can be performed with easily automatable and quantitative methodologies and may be further exploited for patient monitoring, prognosis, diagnosis and probably screening for selected cancers.

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Prostate-specific antigen (PSA) is a glycoprotein produced by the epithelial cells of the prostate. PSA is currently used in clinical practice to facilitate diagnosis and monitoring of prostate carcinoma. The prostate is an organ that possesses androgen, estrogen, and progesterone receptors, and in this respect is similar to the breast. We postulated that breast tumors might also have the ability to produce PSA. We performed these studies on a collection of 525 tumor specimens collected for routine biochemical determination of estrogen and progesterone receptors. Using a highly sensitive immunofluorometric procedure, we measured the p53 tumor suppressor gene product and PSA. Twenty nine percent of the breast tumor extracts contained detectable levels of PSA immunoreactivity (> 0.05 microgram/L). The immunoreactive PSA content was associated with estrogen and/or progesterone receptor-positive tumors (P < 0.002). No association was found between PSA immunoreactivity and levels of the p53 tumor suppressor gene product (P = 0.37). High performance liquid chromatography and Western blot analysis revealed that the PSA immunoreactivity in the tumor had a molecular weight of 30 kDa, similar to that of seminal PSA. Immunoreactive PSA-positive tumors were associated with younger women (P = 0.012) and earlier disease stage (P = 0.064). We postulate that PSA immunoreactivity may be an additional marker of steroid hormone receptor-ligand action.