Present diagnostic techniques do not allow the detection of early metastatic spread of tumor cells, although this spread largely determines the clinical course of patients with small primary cancers, especially lung cancer. To improve the diagnosis of this occult stage of early metastasis, sensitive techniques have been developed that facilitate the detection of isolated lung carcinoma cells in hematopoietic tissues (peripheral blood or bone marrow), or lymph nodes (1 –7 ). It is to be noted that the circulating lung cancer cells from the primary tumor tissue may potentially have different characteristics as compared to the original tumor.
