Cruise, 50, is living with the knowledge that he could die from the same scourge that claimed the life of his father at age 49, reported Showbizspy.
"Tom turned 50 in July, and that's a year older than the age his dad died. With a young daughter to worry about, he has to be thinking about his mortality," a source said.
Cruise's dad Thomas Mapother III died of metastatic rectal carcinoma on January 9, 1984.
Cruise's family had previously voiced concerns when he quickly dropped 15 pounds after Katie Holmes filed for divorce in June.
"His clothes just hang off him. I don't think he's looking after himself," a source said.