Speaking in a video posted on the band's official website, the musician explained that a cancerous tumour had been discovered in his left salivary gland and that he would have to undergo surgery.
"I'm actually going to have to have surgery probably next week, coming up, and then after that [I] have to have some radiation done," he said.
"But the good news is that they did scans of my whole body and it's only localised in this one area, and it's not in a place that affects my voice... I just need a little time to get this in check and then we'll release the record and play some shows."
The Beastie Boys have now cancelled their summer tour plans and delayed the release of their forthcoming album Hot Sauce Committee Part 1, which had been scheduled to hit stores in September.