Riddick, LR, et al. “Palmar and Plantar Keratoderma With Hyperpigmentation and Gynecomastia. Report of a Case Associated With Primary Adenocarcinoma of the Lung”. Acta Dermato-Venereologica, vol. 51, no. 1, Jan. 1971, pp. 69-72, doi:10.2340/00015555516972.