Background: Inflow of tumor cells to circulation is an essential step for metastasis of primary tumors. To know its state may contribute to therapeutic strategy. However, methodology to detect lung carcinoma cells floating in peripheral blood has not been established. Pulmonary surfactant protein (SP)-A, SP-C and Clara cells-10 kd protein (CC10) are specific to the lung and often expressed in primary lung carcinomas. We evaluated the worth of these gene expressions for the detection of carcinoma cells in peripheral blood.
Methods: The expressions in 5 ml of venous blood were tested by RT-PCR. Ninety-nine patients with non-small cell lung carcinoma (NSCLC) and 17 with small cell lung carcinoma (SCLC) were compared to 13 with secondary lung tumor, 48 with non-malignant respiratory diseases and 19 healthy volunteers.
Results: The mRNA expressions of SP-A and SP-C were completely specific to NSCLC when compared to SCLC and secondary lung tumors. All of the healthy volunteers and patients with non-malignant respiratory diseases showed negative for these mRNA expressions, except for one sample. The positive rate of SP-A, SP-C and CC10 mRNA in patients with NSCLC was 33.3%, 14.1%, 3.3%, respectively. The rates of SP-A and SP-C mRNA were higher than that (11.1%) in CEA mRNA. The increased positive rate of mRNA of SP-A and SP-C was significantly dependent on the clinical stage and the existence of distant metastasis.
Conclusion: These results demonstrate that the detection of mRNA of SP-A and SP-C would give clinicians valuable information suggesting the presence of blood-floating carcinoma cells as a step toward metastasis.