Explain Blood Clots With Stage Three Lung Cancer....why. Was Told

Explain blood clots with stage three lung cancer....why. Was told he would need a needle every day in his stomach for blood clots. How could this be happening?
Oxygen and blood clot same day news. What's happening?
Maybe it's a heart problem as well since shortness of breath and blood clots are signs of a bad heart? Can I request a cardiologist. I do NOT have a very compassionate Oncologist...doesn't like to answer questions. I am very worried for my son, age 47. Thank you for any information.