What Causes Vomiting Of Blood Right Before Going Into A Coma?

A person who works along with my husband had severe cold and cough. Was very normal until two days back and was in office. He vomited blood suddenly and was taken to a nearby hospital where he went into coma. He was shifted to an other hospital where they said some fluid is oozing out from back of his brain. They couldn t treat or do a surgery since his platelets count has come down drastically and didn t increase with treatment. They couldn t proceed and he continued to be in coma. He has been declared brain dead this morning. He was tested for dengue and it came out negative. Doctors doubt blood cancer. But can cancer kill a person so fast? What else could be a reason? He was obese but was very active and is just 35.