Review Question - QID 213713

This young patient with a high-grade sarcoma and a family history of breast cancer and leukemia most likely has Li-Fraumeni syndrome, which is caused by a mutation in p53. p53 normally activates pro-apoptotic factors such as Bax, so activity of these proteins will also be decreased.

Apoptosis is a form of programmed cell death that allows for removal of defective or damaged cells. A key mediator of apoptosis is the caspase cascade, which forces the cell to undergo changes such as nuclear fragmentation and mitochondrial permeabilization that result in cell death. This cascade is regulated by pro-apoptotic factors such as Bax and anti-apoptotic factors such as Bcl-2. Notably, Bax is activated by the p53 protein and promotes apoptosis if p53 detects DNA damage. Absence of p53 causes Li-Fraumeni syndrome, which presents with a family history of sarcomas, breast tumors, and leukemias.

Incorrect Answers:
Answer 1: 11;22 chromosomal translocation would be seen in patients with Ewing sarcoma; however, this disease would present as a small round blue cell tumor inside the bone.

Answer 2: Abnormal DNA repair machinery would be seen in patients with BRCA mutations; however, this disease would present with breast and ovarian cancer rather than sarcomas and leukemia.

Answer 4: Decreased activity of Bcl2 protein would be protective against cancer because Bcl2 inhibits apoptotic activity. The activity of this protein is increased in follicular lymphomas.

Answer 5: Increased activity of hamartin protein causes tuberous sclerosis, which can present with multiple different types of hamartomas; however, this disease would not be associated with aggressive cancers such as sarcomas and leukemias.

Bullet Summary:
Pro-apoptotic factors such as Bax are activated by p53 to trigger cell death in damaged cells.