The Wall Street Journal, citing people it did not identify, says Scott Thompson told Yahoo's board and several colleagues of his condition before resigning from his role.
The newspaper says it was told by one source that Thompson's decision to resign was partly influenced by his cancer diagnosis.
Thompson was hired as Yahoo's CEO in January after Carol Bartz's firing.
Yahoo Inc. has named Ross Levinsohn as its interim CEO. Levinsohn ran Internet services within Rupert Murdoch's media empire at News Corp. before Bartz hired him in November 2010
Yahoo's stock gained 33 cents, or 2.2 per cent, to $15.52 in premarket trading Monday.