通信産業従事者における原発性肺癌

30年間の罹患と死亡状況および定期健康診断の意義

抄録

An epidemiological study of primary lung cancer was conducted on NTT workers in the Tokyo area (about 40, 000 persons). During the past 30 years (1960-1989), 77 cases (71 males and 6 females) of primary lung cancer were detected by routine medical examination (radiologic screening by radiophotography at their workplaces) or by clinical symptoms, of whom 59 (54 males and 5 females) were dead as of the end of December 1991.
Standardized incidence rate and standardized death rate of the males by the direct method (5-yr age groups from 20 to 59 yr of age, per 100, 000 population) were 4.5 in the 1960's, 9.9 in the 1970's and 9.8 in the 1980's, and 3.3 in the 1960's, 7.9 in the 1970's and 8.2 in the 1980's, respectively, with increase being observed from the 1970's.
Standardized incidence ratio and standardized death ratio of the males by the indirect method (5-yr age groups from 20 to 59 yr of age) were 107 in the 1970's, 86.8 in the 1980's, and 53.8 in the 1960's, 99.4 in the 1970's and 98.5 in the 1980's, respectively. No significant difference could be observed when compared to the national average.
By histological type, 44 cases of adenocarcinoma, 12 cases of squamous cell carcinoma, 8 cases of small cell carcinoma, 7 cases of large cell carcinoma and 6 cases of other or unclear types were detected. Excluding the 3 unclear cases, of the 77 cases, 54 cases were peripheral type and the remaining 20 cases were hilar type on radiophotography. Peripheral adenocarcinoma was the most common type.
Clinical stage by TNM classification was confirmed in 50 cases, of whom 12 cases were stage I, 5 cases were stage II, 9 cases were stage IIIA, 8 cases were stage IIIB and 16 cases were stage IV.
As for the means of detection, 41 cases were detected by routine medical examination (radiologic screening by radiophotography) and 36 cases were detected by clinical symptoms. The lung cancers of the hilar type could be detected by clinical symptoms at a higher rate than by radiologic screening, but those of the peripheral type were detected at a significantly higher rate by radiologic screening than by clinical symptoms.
The 41 screened cases were detected at an earlier stage and showed a better prognosis than the 36 clinical cases. The rate of operable cases (75.6% in screened cases vs. 30.6% in clinical cases) and 1, 2, 3 and 4-yr survival rates (1 yr 88.6% vs. 41.4%, 2 yr 48.6% vs. 17.2%, 3 yr 37.1% vs. 13.8%, and 4 yr 34.3% vs. 10.3%) were significantly higher in the screened cases than in the clinical cases. Though the 5-yr survival rate was not significantly different between the two groups, the survival curve calculated by Kaplan-Meier method and test by generalized Wilcoxon method showed that the prognosis of the screened cases were better than that of the clinical cases.
Routine medical examination by radiological screening at workplaces is not sufficient to detect lung cancers of the hilar type, but is considered to be effective in detecting lung cancers of the peripheral type. Positive and careful effort should be continued for the detection of early lung cancers in workers.