Mum has cancer, of pelvic area, now a chest infection & blood clots in the lungs the x-ray showed a shadow on her lungs is it the infection or cancer?

Not sure: It could be multiplie things. Could be from blood clot causing infarction or pneumonia or cancer or atelectasis. Would follow or maybe a biopsy to prove what it is. But if she is in treatment then watch and see if the spot goes away with treatment and that may give u an indirect answer.

Cancer: That depends on what type o pelvic tumor. Some gyn cancer spread commonly to the lungs, others don't. She needs a ct o the chest and perhaps a biopsy depending upon the ct results.