Advanced prostate cancer with extremely low prostate-specific antigen value at diagnosis: an example of high dose hook effect.

A 67-year-old man presented with a lower abdominal mass. Radiographic examination revealed a huge mass filling the entire pelvis. Although prostate-specific antigen (PSA) was 1.4 ng/ml, percutaneous needle biopsy revealed adenocarcinoma compatible with prostate cancer, which stained positive for PSA. Hormone therapy was initiated and 1 month later his PSA was as high as 2713 ng/ml, although the mass had decreased in size. High dose hook effect was suspected and hormone therapy was continued. PSA is presently under control and below 0.1 ng/ml. When prostate cancer with very high PSA is suspected and the PSA value is unexpectedly low hook effect should be considered and PSA should be re-analyzed.