The coach, who signed a five-year contract extension worth a reported $35 million with the Celtics this week, is cancer-free, the team said in a Twitter post.
Rivers, 49, has coached the team for seven years, compiling a 56-26 record and guiding the Celtics to four consecutive Atlantic Division crowns.
Boston lost in five games to Miami in this year's Eastern Conference semifinals after sweeping the New York Knicks in the first round.
He also led the Orlando Magic for four-plus seasons, racking up a 171-168 record.
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