A semisynthetic 14-membered ring macrolide antibiotic. Clarithromycin binds to the 50S ribosomal subunit and inhibits RNA-dependent protein synthesis in susceptible organisms. Clarithromycin has been shown to eradicate gastric MALT (mucosa-associated lymphoid tissue) lymphomas, presumably due to the eradication of tumorigenic Helicobacter pylori infection. This agent also acts as a biological response modulator, possibly inhibiting angiogenesis and tumor growth through alterations in growth factor expression. Check foractive clinical trials using this agent. orA protein found on the surface of many different types of cells. It binds to a substance called stem cell factor (SCF), which causes certain types of blood cells to grow. C-kit may also be found in higher than normal amounts, or in a changed form, on some types of cancer cells, including gastrointestinal stromal tumors and melanoma. Measuring the amount of c-kit in tumor tissue may help diagnose cancer and plan treatment. C-kit is a type of receptor tyrosine kinase and a type of tumor marker. Also called CD117 and stem cell factor receptor.