Susceptibility to infection
Many patients with cancer perceive at first a higher susceptibility to respiratory infections, which may add up to their persistent cough and become a productive cough instead. Pneumonia, bronchitis and other viral and bacterial infections might be even more common in lung cancer patients undergoing chemotherapy and radiotherapy, but it sometimes counts as an early symptom as well.
Thus, if you have persistent cough combined with recurrent infections in your respiratory tract, be sure to inform your doctor about such recurrence and your other symptoms so he can perform a thorough investigation of your case.