Basque has a curious situation, in that the differences between “official Basque” and “what people with Basque as their ancestral tongue speak” can be quite large. The majority of the differences are in vocabulary, although some of the “old dialects” use slightly different declinations as well.
My Basque-speaking coworkers use “cancer” (same word as in French and Spanish, although with Basque phonetics and declinations), but checking the official dictionary gives:
1 (Med.) minbizi, bizi, bizien
2 (Astron.) Cancer
Backchecking the medical words produced:
bizi - fast, bright, spry
bizi izan, izaten - live, survive
bizitu, bizi(tu), bizitzen - to become livelier, brighter
So, if you’re trying to pass your Official Basque Language Exam you should use bizien, which derives from a word meaning “fast,” but if you’re talking to someone it would most likely be cancer.