The
epidermal growth factor receptor (EGFR) is overexpressed in 50-70% of human primary breast, lung, and colon
carcinomas, whereas it is not usually expressed in hematopoietic cells. We developed a novel reverse transcription-PCR (RT-PCR)-Southern blot assay for the detection of circulating, EGFR
mRNA-expressing
tumor cells in
carcinoma patients. The assay was set up by increasing the amount of
cDNA step by step in the PCR reaction. The highest sensitivity and specificity were found when using 800 ng of
cDNA in the PCR reaction. Peripheral blood samples from 91 patients with either colon (38), lung (30), or breast (23)
carcinomas and from 38 healthy volunteers were analyzed. EGFR transcripts were found in 44 of 75 (59%) patients with metastatic
carcinoma and in 4 of 38 (10.5%) healthy donors (P < 0.001; chi2 test). The expression of EGFR,
cytokeratin 19, and
carcinoembryonic antigen mRNA in blood samples from patients with metastatic colon
carcinoma was compared. EGFR,
cytokeratin 19, and
carcinoembryonic antigen transcripts were found in 8 of 11 (73%), 3 of 11 (27%), and 5 of 11 (45%) patients, respectively. Furthermore, two of seven (29%) Dukes' B and five of nine (55%) Dukes' C colon
carcinoma patients were found to express EGFR
mRNA in the peripheral blood. All patients that expressed EGFR transcripts in the peripheral blood were found to express the EGFR
protein in the corresponding primary
carcinoma, as assessed by immunohistochemistry. These data suggest that the EGFR assay that we developed is a highly specific and sensitive technique to detect
circulating tumor cells in patients affected by different
carcinoma types.