The game will not be rescheduled.
"The NBA expresses its sympathy to all those affected by the tragedy in Boston earlier today," the league said in a statement.
The Celtics also released a statement:
"Out of respect to all those who have been impacted by the tragic events today in Boston, including members of the extended Celtics family, the Boston Celtics and the NBA have decided to cancel the game scheduled for Tuesday 4/16 between the Boston Celtics and the Indiana Pacers.
"The game will not be rescheduled. Instructions for any fans holding tickets to the game will be provided on Celtics.com after 3 p.m. tomorrow. Our sincere sympathies go out to all those affected by this senseless tragedy. The entire Celtics organization would like to acknowledge the heroic efforts of the brave civilian, police, fire and medical personnel responding today in the City of Boston."
The game was set to be the second-to-last for both teams. But with both the Celtics and Pacers already cemented into their playoff positions, the league opted to just cancel the game.