Unilateral breast edema usually signifies an underlying pathology of the breast and prompts extensive investigations for the purpose of an early treatment. Although breast edema has been reported with other systemic etiologies, it has not been described in patients with lung cancer. We report two cases of unilateral breast edema occurring in patients with non-small cell lung cancer and ipsilateral pleural effusion. Mammography and ultrasound of the breast both revealed increased interstitial density suggestive of fluid retention without any underlying masses. We performed a therapeutic pleurocentesis on one patient for symptomatic relief, and there was simultaneous improvement of the breast edema. We postulate a possible pathophysiology for the association between breast edema and malignant pleural effusion. The principle of management when one encounters similar cases would be to treat the underlying pleural effusion.