REVERSE TRANSCRIPTASE POLYMERASE CHAIN-REACTION ANALYSIS OF PARATHYROID HORMONE-RELATED PROTEIN FOR THE DETECTION OF TUMOR-CELL DISSEMINATION IN THE PERIPHERAL-BLOOD AND BONE-MARROW OF PATIENTS WITH BREAST-CANCER/

Tumor cell dissemination in the bone marrow is an independent prognost ic marker for relapse and survival for patients with primary breast ca ncer. Parathyroid-hormone-related protein (PTHrP) is expressed in most . primary tumors and bone metastases of patients with breast cancer. P THrP acts as an autocrine growth factor for breast cancer cells in vit ro and there is evidence that it is especially important for osseous m etastasis. For a sensitive detection of PTHrP-positive disseminated tu mor cells a reverse transcriptase/polymerase chain reaction (RT/PCR) a ssay for PTHrP transcripts in the peripheral blood (PB) and in the bon e marrow (BM) has been established. In mixing studies, the sensitivity of the reverse transcriptase/polymerase chain reaction (RT/PCR) for P THrP was one tumor cell in 1 x 10(6) mononuclear cells. At this level of sensitivity, transcripts of PTHrP were detected in none of 30 PB sa mples and in 3 of 25 BM samples of healthy volunteers; there were also no transcripts of PTHrP in the PB and BM of 6 patients with benign br east lesions. The PB samples of 31 patients and the BM samples of 34 p atients with predominantly early-stage breast cancer were tested for P THrP expression along with immunocytology against cytokeratin 18 (CK18 ) as a standard immunological detection technique. PTHrP expression wa s shown in 9 of 31 patients in the PB and in 9 of 34 patients in the B M. In 30 patients, PB and BM samples were available simultaneously. Th ere were cases of combined positive findings in the PB and the BM (4/3 0) and of isolated positivity in the PB (5/30) or in the BM (4/30). Co mpared to immunocytology, RT/PCR assay of PTHrP assay was significantl y more sensitive in the peripheral blood (8/30 by RT/PCR compared to 1 /30 by immunocytology). In the bone marrow there were cases of positiv ity for both markers (2/34), cases of isolated positivity by immunocyt ology for CK18 (3/34) and cases of isolated positivity for PTHrP trans cripts (7/34). In conclusion the RT/PCR assay for PTHrP transcripts is a feasible and very sensitive technique for the detection of tumor ce ll dissemination in the PB, even in patients with early-stage breast c ancer. The specificity of detection of PTHrP transcripts in the bone m arrow is limited, possibly because of autochthonous expression of PTHr P in osteoblastic cells. The clinical follow-up of the subgroups of pa tients at risk, as defined by this assay, will show its prognostic sig nificance for patients with breast cancer.