Chemotherapy lowers the white blood cell count or weakens the immune system for a long time. This puts the patients at a high risk of getting a serious fungal infection of the internal organs or blood. One of these infections is caused by a mold called Aspergillus and can be life threatening. Usually doctors give preventive antifungal therapy to try to lower the risk of this infection. Despite this, patients are still at risk of getting fungal infection. This study is thus designed to test Galactomannan - a component of cell wall of Aspergillus and hence detect and treat fungal infection early.