An association between sputum eosinophilia and carcinoma of the lung: a study of 549 patients.

A prospective 11 year study of sputum cytology in 5,475 patients with respiratory diseases other than asthma or Loeffler's syndrome showed that carcinoma of the lung was the commonest single condition associated with a sputum eosinophilia: it occurred in 68 (12.4%) of the 549 patients with pulmonary carcinoma. While clearly not a diagnostic finding, sputum eosinophilia should stimulate, in appropriate cases, a further search for carcinoma. The cause or causes of the eosinophilia are not known at present but the body's reaction to malignancy is a topical subject of study worldwide.