Frequency of expression of prostate-specific antigen mRNA in lung tumors.

The presence of prostate-specific antigen (PSA) protein and messenger RNA (mRNA) was studied in 52 primary lung tumor tissues. The PSA protein was detected more frequently and at higher levels in lung tumor extracts from men. The levels of PSA protein in tumor extracts correlated with preoperative and postoperative serum PSA levels, suggesting a possible contamination of the tumor extracts with PSA from residual blood in the tumor vasculature. The PSA mRNA was detected by reverse transcription-polymerase chain reaction (RT-PCR) and Southern blot hybridization in 24 (68%) of 35 tumors from men, in 9 (53%) of 17 tumors from women, and in 5 (71%) of 7 adjacent normal lung tissue specimens. The levels of PSA protein did not associate with patient age, the tumor stage, grade, or histologic type, or the nodal status. Similarly, PSA mRNA was not associated with any clinicopathologic variables, but squamous cell carcinomas, especially in men, were more frequently positive. A by-product of the RT-PCR procedure was cloned and sequenced and found to be a 450-base pair sequence not previously deposited in the data bank. We conclude that PSA mRNA and protein frequently can be detected in lung tumors and normal tissues from men and women but at levels much lower than those seen in breast carcinomas in women. The significance of the new 450-base pair sequence remains to be determined.