Kanye West's father, Ray West, is battling cancer ... TMZ has learned.

Sources close to Ray tell us he's been diagnosed with prostate cancer -- not stomach cancer as has been widely reported. We're told Kanye dropped everything to help his dad upon hearing the news.

Ray is currently being treated in L.A., and sources say he's responding well. We're being told that, for now, it looks like he's going to be okay.

The diagnosis comes just over 10 years after the death of Kanye's mother, Donda, to whom he was very close and whose death helped trigger his mental breakdown in 2016. 

Ye and his pops were spotted grabbing lunch at Nobu Malibu in March ... a rare sighting of the father and son together. 

Ray and Kanye's late mother divorced when Ye was a young child, but the 2 remained amicable over the years.