Atopy and primary lung cancer. Histology and sex distribution. Atopy, defined as the ability to develop IgE antibodies to commonly encountered allergens under conditions of normal exposure, has an inherited component with pleiotropic effects. An inverse relationship between the occurrence of atopy, allergy-related diseases, and cancers at specific sites has been reported. The familial association of primary lung cancer is most evident among women, nonsmokers, and those with adenocarcinomas. In order to determine whether the relationship between a lower prevalence of atopy among patients with lung cancer compared to control subjects was consistent between histologic cell types, we used seven common allergens to allergy prick skin test 209 community control subjects (46 women), 109 cases with primary squamous cell carcinoma of the lung (25 women), and 67 patients with primary adenocarcinomas of the lung (23 women). We have confirmed earlier reports of an inverse relationship between atopy and lung cancer risk. In analyses focusing on sex and histologic cell type, we found that women with adenocarcinomas were an exception and were as likely to be atopic as control subjects. The evidence does not support a protective role for atopy among these women. 