Most tumors originally diagnosed as poorly-differentiated malignancies are indeed malignant histiocytomas. The histologic features of malignant histiocytomas are directly related to soft-tissue sarcomas, a collection of cancers of the connective tissues. They tend to appear as pseudo-encapsulated fleshy tumors, but have poorly defined margins and are capable of local infiltration Local recurrence after conservative surgical excision is common. They generally have a poor response to chemotherapy and radiation therapy for measurable disease. In those patients, there is a defect in one of their oncogenes that normally produces a protein that works to suppress cell division.
Cancer is essentially a result of uncontrolled cell division.
This malfunctioning oncogene predisposes these patients to cancers, particularly soft-tissue sarcomas, and several other malignancies, all occurring at unusually young ages. Multiple cancers often occur independently in an individual dog. In Li-Fraumeni patients, the gene p53 which produces the p53 protein which normally acts to suppress cancer, has been found in a mutated form. The p53 protein has the ability to instruct the cell to stop cell division or cause death of the cell if the division is already advanced. When this protein has mutated, cell division is unrestricted and malignancies develop.