Recurrent pneumonia question. What makes it come back? Could there be a tumor?

Mnay things. This requires medical evaluation by a doctor, several possibilities. A list would include: a error in diagnosis, for example congestive heart failure, & inflammatory diseases of the lungs can mimic recurrent pneumonia. ("boop" for example) exacerbation of COPD can also be confused with pneumonia. Repeat pneumonia can be caused by a tumor obstructing the airway, and immune system problems.