CA9 and neoplasm: CA IX is one of the few tumour-associated CA isoenzymes known so far; it is highly overexpressed in a broad range of solid tumours (carcinoma of the cervix, kidney, breast, lung, head and neck and tumours of the brain)5 yet has only a very limited distribution in normal tissues (e.g. gastrointestinal tract – epithelia of the glandular stomach, small intestine and gallbladder).6