The present invention relates to: —use of a 2,3-dihydroimidazo[1,2-c]quinazoline compound, or of a pharmaceutical composition containing same, as a sole active agent, or of a combination of a) said compound or a pharmaceutical composition containing said compound and b) one or more further active agents, for the preparation of a medicament for the treatment or prophylaxis of cancer; —combinations of a) said compound and b) one or more further active agents; —a pharmaceutical composition comprising said compound as a sole active agent for the treatment of breast cancer; —a pharmaceutical composition comprising a combination of a) said compound and b) one or more further active agents; —use of biomarkers involved in the modification of Bel expression, HER family expression and/or activation, PIK3CA signaling and/or loss of PTEN for predicting the sensitivity and/or resistance of a cancer patient to said compound and providing a rationale-based synergistic combination as defined herein to increase sensitivity and/or to overcome resistance; and —a method of determining the level of a component of one or more of Bcl expression, HER family expression and/or activation, PIK3CA signaling and/or loss of PTEN.