Heterogeneity of tumor cells

Investigations of cell clones isolated in vitro, or selected in vivo, have shown that tumor cell populations are heterogenous. The isolated cell clones or cell subpopulations originating from a single tumor may differ in a variety of biological and biochemical characteristics. Genetic lability and selective pressure are the most probable mechanisms by which a proliferating tumor cell population becomes heterogenous. Differences in drug sensitivity of cell subpopulations within a tumor represent a major limitation in tumor sampling procedures for tests predictive of effective chemotherapy. Different drug sensitivity was found when comparing human cancer cell samples from a primary solid tumor with those obtained from ascites, different metastatic nodes, or even in samples from different areas within the same tumor.