Dikembe Mutombo starting treatment after brain tumor diagnosis 1:16 PM ET ESPN News Services Dikembe Mutombo is undergoing treatment for a brain tumor, the NBA announced Saturday on behalf of the Hall of Fame center and his family. The NBA said in a statement that Mutombo -- who ranks second in NBA history for career blocks -- is beginning treatment in Atlanta and is in "great spirits." "Dikembe and his family ask for privacy during this time so they can focus on his care," the league said. "They are grateful for your prayers and good wishes." Mutombo played 18 NBA seasons for the Denver Nuggets , Atlanta Hawks , Philadelphia 76ers , New Jersey Nets , New York Knicks and Houston Rockets before retiring after the 2008-09 season. He was the league's top defensive player four times and played in eight All-Star games over 18 seasons. Mutombo ranks 17th in rebounds (12,359) and finished with 3,289 career blocks, second to Hakeem Olajuwon (3,830). Mutombo followed most blocks with a playful wag of his right index finger, a gesture that became his enduring signature. Following his playing career, Mutombo has served as an ambassador for the sport, particularly in the development of the Basketball Africa League, which completed its second season in May. He was inducted into the Naismith Memorial Basketball Hall of Fame in 2015. Information from The Associated Press was used in this report.