I .
to make new and important discoveries :
Scientists think they are beginning to break through in the fight against cancer.
—related noun breakthrough
II .
break through | ˌbreak ˈthrough sth
1.
to make a way through sth using force :
Demonstrators broke through the police cordon.
2.
( of the sun or moon ) to appear from behind clouds :
The sun broke through at last in the afternoon.