Objective: To describe the chromosomal numerical changes present in primary prostate tumours and their matched lymph-node metastases, to identify a clonal cell migration process which could account for the metastatic behaviour.
Materials and methods: Twenty-eight cases of unsuspected stage D1 (pT2-3pN1M0) prostate cancer were detected among patients who had a radical prostatectomy for clinically localized prostate cancer. Fluorescence in situ hybridization (FISH), using centromeric probes to enumerate chromosomes 7, 8, 10 and 12, was used to assess numerical chromosomal changes. FISH analysis was used on isolated nuclei obtained from matched primary tumours and their lymph node metastases.
Results: Of the 28 suitable cases it was possible to complete the study in 18 pairs of matched tissues; the remainder were excluded because of insufficient tissue or poor preservation of at least one of the tissues. There was cytogenetic change (aneuploidy) in 16 of the 18 primary tumours, the most common being monosomy 8, detected in 14, followed by trisomy 7, in 13 aneuploid tumours. All lymph node metastases were aneuploid by FISH. As in the primary tumours, monosomy 8 and trisomy 7 were the most common cytogenetic alterations, in 13 and 15 of the lymph node tissues. FISH analysis showed a high correlation (83%) in the cytogenetic pattern of changes between the primary tumours and their lymph node metastases. Moreover, a similar number of cells had the most common aneusomies when comparing prostate and the lymph node tissues.
Conclusions: These results show a similar pattern of cytogenetic alteration in the primary tumour and its lymph node metastasis, characterized by the frequent presence of trisomy 7 and monosomy 8, suggesting that clonal cell selection is not involved in the metastatic process.