Cells within tissues are undergoing various phases of the cell cycle at different times. In some tumors, the cells are cycling rapidly, but in others, the proliferation rate is slow. Traditionally, cytogenetic laboratories have harvested live (unfixed) tissue and cultured it to obtain dividing cells, which are then used to perform FISH studies. There are drawbacks to performing traditional cytogenetic FISH on human solid tumors, including:
- No growth in culture - Not all tumor cells are rapidly dividing and may not grow in culture.
- Overgrowth in culture - "Tumors" removed during surgery are composed of a mixture of both abnormal and malignant cells and normal and connective tissue cells. Connective tissue can tend to overgrow in culture, choking out normal and abnormal cells and preventing them from growing.