mrcem2-1859

A 62-year-old woman presents with a persistent cough that has been ongoing for several months. She reports that the cough occasionally produces a small amount of phlegm, especially in the morning. She has experienced a significant weight loss of 28 pounds over the past six months and constantly feels fatigued. Even with minimal physical activity, she becomes short of breath. She has no significant medical history and is a non-smoker. She enjoys keeping and racing pigeons as a hobby. Upon examination, bilateral fine end-inspiratory crackles are heard.

What is the SINGLE most likely diagnosis?