Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: There has been marked decrease in a left hilar mass . The right lung remains clear without pleural effusion . On the left , there is an increased volume loss at the left lung base with a pleural effusion and posterior opacity which may represent atelectasis or pneumonia .
    OUTPUT:
    
Markedly improved left hilar mass , but increased left basilar opacification with pleural effusion suggesting atelectasis or pneumonia .