The Apparent Sites of Origin of Carcinomas of the Lung

Carcinomas of the lung originate chiefly in the epithelial lining of the bronchial tree. It has frequently been reported that most of them arise in the main and lobar bronchi. These observations, however, are based largely on surgical or necropsy material and unavoidably include many cases in which the tumor measures several centimeters in diameter and has “obliterated” its point of origin. Rigler (9) has observed that some bronchial carcinomas grow eccentrically so that what may present to the radiologist as a “hilar” tumor, or to the bronchoscopist as a lobar bronchus tumor, has in fact arisen in a segmental or subsegmental bronchus and extended centrally. The precise locus or site of origin of bronchial cancer is of interest to students of the air pollution theory of lung carcinogenesis. The concentration of inhaled gaseous or particulate materials should be greatest in the trachea and, in healthy lungs, smallest in the terminal bronchioles, with variable gradations in the intervening bronchi. For some unknown reason, carcinoma of the tracheal epithelium is quite rare. It has been reported that carcinoma of the bronchus occurs in descending order of frequency from the main to the subsegmental divisions. What are the facts? Efforts to find well documented data on the more common sites of origin of localized lung cancer proved unrewarding. It was therefore decided to review a series of cases in an attempt to answer the question. Method The records of patients having a diagnosis of bronchogenic cancer were reviewed at four hospitals in San Francisco (San Francisco General Hospital, St. Joseph's Hospital, French Hospital, and Letterman Army Hospital). So far as possible, consecutive case records for approximately the past five to ten years were reviewed. The radiographic, bronchoscopic, surgical and/or pathologic descriptions of each case were analyzed and an attempt was made to identify or pinpoint the apparent site of origin of each tumor. Where possible, the roentgenograms were reviewed and the bronchologist's diagrams were studied. In some instances gross surgical and necropsy material was available for examination. Needless to say, most of the necropsy material consisted of tumors too large to permit reasonable deduction as to the primary locus. Often, the gross surgical or surgical-pathologic description failed to indicate whether the lesion arose in a bronchus or in adjacent lung tissue. Even with extensive study it was sometimes impossible to ascertain this point; occasionally, it was fairly definite that a lesion had originated in a subsegmentai bronchus and then grown into an adjacent main or lobar bronchus.