What defines the recessive effect of tumor suppressor genes in cancer?

The recessive effect of tumor suppressor genes is defined by the requirement that both alleles must be mutated for the normal regulatory function of the gene to be completely lost. Tumor suppressor genes play a crucial role in controlling cell division and preventing tumor formation. When one allele of a tumor suppressor gene is mutated, the remaining functional allele can often still compensate for the loss, allowing normal control of the cell cycle.

Only when both alleles are mutated does the mechanism that typically suppresses uncontrolled cell growth fail. This is why many cancer types, such as retinoblastoma and certain forms of breast cancer involving the BRCA1 and BRCA2 genes, are linked to the biallelic inactivation of tumor suppressor genes. In contrast, a single mutation in the tumor suppressor gene may not be sufficient to influence cancer development significantly.

The requirement for both alleles to be mutated highlights the importance of these genes in maintaining cellular homeostasis and why their malfunction can lead to cancer.