This is the familial neoplasm. Familial neoplasms have neoplasm-causing mutations ransmittedthrough the germ line. Familial neoplasms account for about 5% of all cancers and they are mendelian disorders. They are often inherited in autosomal dominant pattern with few exceptions.
They are caused by mutations that affect proteins which regulate cell growth. And they are exemplified by neurofibromatosis types 1 and 2. It should be noted that most cancers are not familial and these non-familial cancers are caused by mutations of tumor-suppressor genes, proto-oncogenes, and apoptosis- regulating genes in somatic cells. Hence, these mutations are not passed in the germ line. Therefore, most cancers are not mendelian disorders i.e. they are sporadic or nonfamilial disorders.
1. Neurofibromatosis type 1
This was previously called von Recklinghausen disease. Has autosomal dominant transmission in 50% of cases. (The rest 50% are due to new mutations. Has extremely variable expressivity but the penetrance is 100%.This is due to a mutation in the NF1 gene (which is a tumor-suppressor gene).
This mainly shows neurofibromas in the skin and other locations, café au lait spots (i.e. light brown skin pigmentations), and pigmented iris hamartomas (Lisch nodules). The benign neurofibromas can sometimes become malignant. May also show skeletal disorders such as scoliosis and bone cysts and increased incidence of other tumors especially pheochromocytoma and malignancies such as Wilm’s tumor, rhabdomyosarcoma, and leukaemia.
2. Neurofibromatosis type 2
This was in the past called acoustic neurofibromatosis. Neurofibromatosis type 2 is much less common than neurofibromatosis type 1. Neurofibromatosis type 2 is an autosomal dominant disorder. Neurofibromatosis type 2 is due to a mutation of the NF-2 gene (which is a tumor suppressor gene) shows bilateral acoustic schwannomas, multiple meningiomas, and gliomas (typically ependymomas of the spinal cord).