There is a partially loculated right pleural effusion. There are increased reticulonodular markings throughout the left lung field.

Left pleural space clear, bones appear normal.

This is a primary lung cancer with malignant pleural effusion and lymphangitis carcinomatosa on the left side.

Lymphangitis carcinomatosa / carcinomatosis is a malignant infiltration of the pulmonary lymphatics.
Frequently associated with lung cancer, but also breast, stomach, pancreatic and prostate.
Oral corticosteroids and diuretics can have transient benefit, but usually this is part of a rapid decline.