A primary cell culture is the initial culture set up directly from a body tissue. Primary cancer cultures can be initiated and derived from a variety of tissue types such as solid tumor fragments (primary or metastatic) or cell suspensions, for example, aspirates, including peritoneal ascites or pleural effusions. Cell suspensions can be particularly convenient for developing cell lines as they are already growing as single cells or clusters, avoiding the need for mechanical or enzymatic dispersion. The cellular composition of primary cultures is often very variable with hematopoietic and stromal cell types contributing to the cellular mix. Fibroblasts, in particular, can be problematic as they attach readily to matrices and often outgrow the cancer cell population. Cancer cells differ from most normal cell types in their ability to grow in suspension, for example, in agar, but generally cultures are initiated by allowing cells to adhere to a substrate before proliferating. A number of strategies have been developed to help disperse fragments of tissue and these include mechanical and enzymatic methods (see Subheading 1.2.).