Detection of genomically-tagged cancer cells in different tissues at different stages of tumor development: lack of correlation with the formation ofmetastasis

Genetic detection of tumor cells in blood, lymphatic nodes or bone marrow u sing reverse transcription and polymerase chain reaction (PCR) is quite att ractive because it allows the early diagnosis of cancer dissemination. Unfo rtunately, this type of detection strategy cannot be applied to solid paren chymas, because they usually share with tumor cells the mRNA markers. To av oid this impediment, we have developed an experimental model of cancer usin g cells with a genome-associated tag. DHD/K12-PROb cancer cells were stably transfected with pcDNA3.1CAT. Approximately 10(6) transfected cells (DHD-C AT cells) were injected subcutaneously into the chest of BD-UC rats. Animal s were divided into 11 groups according to the time between injection of tu mor cells and euthanasia. An additional 'untagged group' was injected with untransfected cells (DHD-Wild), Blood and tissues samples were collected af ter euthanasia, Macroscopic and microscopic analysis was done. To detect ci rculating tumor cells or their presence in peripheral organs, we performed PCR with nested primers to amplify chloramphenicol acetyl transferase-encod ing (CAT-encoding) DNA sequences. The minimum number of cells that yielded detectable cells routinely was 2 in 10(6). No modification of cancer aggres siveness was observed in DHD-CAT cells. DHD-CAT cells were detected by PCR in lung from the ist week after inoculation, in liver, spleen and kidney fr om the 3rd week and in the blood from the 5th week, All animals analyzed 12 weeks after injection showed lung metastases. Metastases in liver, spleen or kidney, either microscopic or macroscopic, were never detected. We have developed an experimental model of cancer based on genomic tagging of tumor cells that allows the detection of small numbers of cells in all organs an d the blood. The presence of cancer cells in parenchymas detected with mole cular technology does not correlate with the development of clinically rele vant metastases. (C) 1999 Published by Elsevier Science Ireland Ltd. All ri ghts reserved.