Purpose: The reverse transcriptase polymerase chain reaction (RT-PCR) assay for prostate specific antigen (PSA) expressing cells in the blood circulation has been under intense investigation since 1992. Although it has been suggested that this technology could be used as molecular staging for occult prostatic hematogenous metastases, we have been unable to confirm RT-PCR PSA positivity of peripheral blood to predict stage or recurrence in radical prostatectomy cases. We performed bone marrow RT-PCR PSA assay on a large cohort of radical prostatectomy cases and evaluate the use of this assay in improving prostate cancer staging and detecting early recurrence.
Materials and methods: Unilateral anterior iliac crest bone marrow aspirates were performed on 116 patients immediately before radical prostatectomy between February 1995 and September 1997. Radical prostatectomy specimens were processed as whole mounts. A sensitive nested RT-PCR assay with specific primers derived from the PSA sequence was used, which enabled us to detect PSA expressing LNCaP prostate cancer cells at the sensitivity of 1 cancer cell per 10 million lymphocytes (1/10(7)). A minimum of 3 RT-PCR PSA reactions were performed on all patients and at least 2 positive tests were required to define positivity. Patients were followed for PSA recurrence (mean followup 14.7 months).
Results: PSA expressing cells were detected in bone marrow of 51 of 116 patients (44.0%) when at least 2 of 3 RT-PCR PSA assays per patient were positive. A much higher rate of RT-PCR PSA positivity was noted (77/116 patients, 66.3%) when any RT-PCR PSA positivity was considered. In 10 randomly selected cases the RT-PCR product was confirmed as PSA by deoxyribonucleic acid sequencing. Of 51 bone marrow RT-PCR positive cases 25 (49%) had organ confined disease and 26 (51%) had nonorgan confined disease. Similarly, bone marrow RT-PCR PSA was not associated with age, race, grade, pretreatment PSA or prostatic acid phosphatase value, clinical stage or margin status. However, the 2-year disease-free survival was 96.6% in RT-PCR negative patients versus 77.5% in RT-PCR positive patients (p = 0.054), and bone marrow RT-PCR PSA was an independent prognostic factor in multivariate analysis including PSA, Gleason grade and pathological stage.
Conclusions: Bone marrow RT-PCR PSA positivity in this study did not predict pathological stage, grade or margin positivity as determined from whole mount prostate cancer specimens. Furthermore, no relationship with age, grade or serum markers and bone marrow RT-PCR PSA positivity was noted. However, bone marrow RT-PCR PSA was associated with early disease recurrence. Further studies and longer followup are warranted to define the metastatic potential of the PSA expressing cells in the bone marrow of prostate cancer patients.