In a study of 505 cases of lung carcinoma from a period in which there was a significant change in tobacco-smoking habits, a dramatic shift in the histologic type and location of the lung tumors was observed. Peripheral tumors, found in 30.7% of the carcinomas occurring before 1978, were found in 42% of the carcinomas from 1986 to 1989. The corresponding decrease in the centrally originating bronchial carcinoma was from 69.3% to 57.3%. The greatest change in histologic cancer type was that the incidence of bronchioloalveolar carcinoma more than doubled from 9.3% in the earlier period to 20.30/b percent in the 198640-1989 period. Corresponding to the decreasing incidence of lung carcinoma, there is a decrease in cancers related to cigarette smoking. A study of cases of lung carcinoma among nonsmokers and former smokers showed a decreased incidence of the bronchiogenic cancers and an increase of cancer occurring in the peripheral lung parenchyma. This finding should be validated in other population-based studies, and if confirmed, new studies should be undertaken in an attempt to discover the factors that play a role in the devclopment of such cancers. As an example, viral oncogenes may be a possibility. Viruses were suggested in the past as being related to the development of some of these tumor types. Cancer 68:1973-1977,1991.
ARCINOMAS arising in the peripheral parenchyma C of the lung with no bronchial involvement may have a different cause than bronchogenic carcinomas: they have not been related directly to exposure to tobacco smoking habits or any other known carcinogenic agents. Over several years investigators reported differing trends in the incidence of the histologic types of carcinoma of the lung, sometimes indicating a relative increase of adenocarcinoma compared with the squamous cell type. Adenocarcinomas are associated less directly with tobacco use or any other known carcinogens. However, adenocarcinoma is also the lung tumor type that is often not bronchogenic but develops in the peripheral parenchyma of the lung. We observed an increased incidence of carcinomas ansing in the periphery of the lung compared with bronchogenic tumors of all types.
Primary peripheral lung tumors are those ( 1 ) that arise in the lung parenchyma beyond the bronchi where there is no association with any bronchus and (2) for which the From the *Veterans Administration Hos2ital. East Orange.