Evidence of heterogeneity within colorectal liver metastases for allelic losses, mRNA level expression and in vitro response to chemotherapeutic agents.

A goal of oncology is to predict chemosensitivity of tumors. This approach assumes that in a patient all tumor deposits are homogeneous. We have tested the heterogeneity between several samples of the same liver metastasis (LM; intrametastatic heterogeneity) or between multiple LM (intermetastatic heterogeneity) from colorectal cancer in a single patient. In 16 untreated patients, several fragments of LM and nontumorous liver were collected. Heterogeneity to anticancer drug treatment was assessed in vitro on primary tissue cultures on poly-HEMA-coated surface with or without the topoisomerase-I inhibitor metabolite SN-38. Heterogeneity of response to SN-38 was observed in 55% of cases from one fragment to another in the same LM and in 64% of cases from one LM to another in the same patient. Allelic losses were characterized on 5q, 8p, 17p, 18q, 22q using 29 microsatellites markers. Seven patients (58%) had a perfect homogeneity for allelic losses in their LM whereas 3 (21%) had intrametastatic and 2 (18%) had intermetastatic heterogeneity. The analysis of gene expression was carried out by real time RT-PCR quantification using specific probes for TS, TOPO1, ERCC1, and CES2. Level expression of genes tested appeared heterogeneous with average variations of 57(±23)%, 52(±18)%, 53(±18)%, 56(±16)% for TS, TOPO1, ERCC1, and CES2 respectively for intermetastatic variability and 47(±26)%, 36(±14)%, 38(±19)%, and 56(±29)%, respectively for intrametastatic variability. Our results demonstrate intermetastatic and intrametastatic heterogeneity suggesting that pretherapeutic analysis of a single tumor biopsy is likely to lead to a misinterpretation of sensitivity to anticancer treatment.