What factors could cause two pets to have cancer at the same time?

I have a white cat who is 13 years of age. She had a malignant tumour on her eyelid. Had another cancer above her eye of a different kind. Had eyelid one has been removed twice, no sign of return yet however the one above the eye is coming back slowly. She also has a heart murmur but I put that down to old age.

Today I found out my dog has breast cancer. She is 12 years old and otherwise healthy until this point. Her breathing has always been heavy after exercise but has gotten worse which is why we took her to the vet. She has a rotten tooth right at the back (Went unnoticed, front teeth all ok) and the vet said this could cause the breathing issue so hopefully the cancer has not spread.

Is there any factors in my household that may be causing this? I know my cat being white would be one, and my dog wasn’t desexed before she first when on heat which increases the risk.

Im curious as to whether anyone has had this happen and how they dealt with it. Any insight and advice is welcome.