Inaccuracies in certification of nonmelanoma skin cancer deaths

Nonmelanoma skin cancer is the most common cancer site in the United States, yet mortality from this cause is poorly understood. We sought medical records of the 116 reported deaths during 1979 through 1987 from this cause (International Classification of Diseases, 9th version [ICD-9], code 173) among Rhode Island residents to evaluate the accuracy of the reported cause of death. Of the 110 cases for which the cause of death could be classified as correct or incorrect, 59 (54%) were misclassified, 49 (83%) of which were mucous-membrane, squamous-cell carcinomas of the head and neck. For most of these, the written death certificate diagnosis was squamous-cell carcinoma of the head and neck, which was coded 173.4. Other problematic diagnoses were cancer of the head and neck and malignant fibrous histiocytoma. In response to a mailed survey, most health departments replied that squamous-cell carcinoma of the head and neck was coded under rubric 173 and malignant fibrous histiocytoma was coded under rubric 171, but there was no unanimity. The misclassification of other causes of death to ICD-9 rubric 173 is substantial. The vast majority were coded to rubric 173.4 and were due to a small number of diagnoses that are recognizable on examination of the death certificate.