胃集検における偽陰性例の検討―モデル地区5年間の成績を中心にして

A Study of False-Negative Cases in Mass Survey for Gastric Lesions: With special reference to five years' results in a model district

　胃集団検診は今や全国的に普及し，方法論的には間接X線撮影法，被爆線量，能率面あるいは読影法など多岐にわたる検討がなされ，ほぼ確立された感さえある．そして，発見胃癌中に占める早期癌頻度の増加あるいは外来発見胃癌に比してその予後がすぐれている点など胃癌発見のみならず治療面からも胃集検の有用性は多くの報告者により立証されている．

　しかし，多くの健康で無愁訴な集団を対象として，間接X線フィルムに描出される所見のみを唯一の情報としてスクリーニングを行う胃集検には，従来から見逃し例，見落し例あるいは誤診例などとして報告されているように偽陽性例，偽陰性例の存在することは十分予測されるところであり，X線技師を中心にパラメディカル従事者は最良の撮影像を得るべく努め，読影者はより正確な読影を心がけ，スクリーニング能向上に努力している現状であろう．

　Five years' results in the mass survey between 1972 and 1976 in a remote island selected as a model district were reviewed and false-negative cases were investigated.

　The population of the district totaled approximately 20,000 and the over-all number of people received examination during the period of five years was 7,672. Close examination was necessary in the ratio of 27.9 per cent which appeared to be relatively high. The real number of the close examination received was 1,640 (76.0 per cent).

　False-negative cases were composed of one advanced cancer and three early cancers. Two of the latter were detected by the examination in the following year. The remaining one was proved by medical reports from the district. Gastric cancers detected in this survey were seven early and nine advanced ones, and the ratio of false-negative cases was 20 per cent. Advanced cancers in these twenty cases were detected by only once examination except for an occasion. Early gastric cancer, on the other hand, was mostly found by year after year examinations. In the interpretation of indirect X-ray films, nine cases of advanced cancer were found by abnormal findings consistent with those at the location of cancer. One false-negative case was due to misinterpretation of films.

　On the contrary, one out of seven early cancers was due to misreading of the location of cancer, and abnormal findings in the remaining six cases were possible to point out in the review of films. In two of three false-negative cases of which lesions were found in the following survey, it was impossible to point out abnormalities even in the review of films at the previous mass survey.

　In conclusion, false-negative cases were due to misinterpretation of films or due to a limitation in the reading of indirect X-ray films. That is, year after year examinations are necessary in order to detect early gastric cancer even in mass survey.