Final answer:
True, many familial cancers are due to germinal inheritance of mutant alleles in TSGs, such as BRCA1/2 genes, leading to increased cancer risks, notably in breast and ovarian cancer, and conditions like Li-Fraumeni syndrome with a mutated p53 allele.
Step-by-step explanation:
The statement many familial cancers can be explained by germinal inheritance of a mutant allele of TSGs (tumor suppressor genes) is true. When mutations occur in germ cells, these mutations are passed on to the next generation, leading to a predisposition to certain cancers. An example of this is mutations in the BRCA1 and BRCA2 genes, which greatly increase the risk of breast and ovarian cancers in women. In the case of Li-Fraumeni syndrome, individuals inherit a mutated p53 allele, leading to a significantly increased risk of various types of cancer.