免疫学的便潜血テスト陰性大腸癌の特徴

Characteristics of Colorectal Cancer with Negative Immunological Fecal Occult Blood Test

要旨　全大腸内視鏡検査当日の朝採取した便に対して逆受け身赤血球凝集法（以下RPHA）による便潜血テストが実施された深達度sm以深の単発大腸癌103症例に対して，免疫学的便潜血テスト陰性大腸癌の特徴を明らかにするために，病巣の存在部位，大きさ（最大径），深達度，肉眼形態などについてRPHA陽性率（感度）の検討を行った．最も強い関連性を示したのは病巣の大きさであり，特に最大径10mm以下の5病巣ではRPHA感度0，11mm以上20mm以下の16病巣では38％であったのに対し，21mm以上30mm以下の20病巣では75％と，統計学的に20mmを境にして有意差が認められた．すなわち大腸癌診断法としての免疫学的便潜血テストは，20mmを越える大腸癌には有用であるが，20mm以下の病巣ではたとえ進行癌であっても過半数が偽陰性となる可能性が高いことが示唆された．

　One hundred and three solitary colorectal cancers with submucosal or further invasion were evaluated for the characteristics of colorectal cancer with negative immunological fecal occult blood (IFOB) test. A stool specimen was collected and examined by the reverse passive hem agglutination (R-PHA) method on the same day of total colonoscopic examination. The sensitivity of IFOB test was analyzed by the factors such as the location, size (maximal diameter), invasivity, macroscopic shape of cancers. Twenty seven patients (26.2%) underwent total colonoscopic examination for health care check (screening group) and 76 patients did so for evaluating some abdominal symptoms (hospital group). The age of the patients of screening group was 58.0±10.3 years old and that of hospital group was 66.1±10.7 years old. The size of cancer was most strongly correlated with positive IFOB test among these factors. Sensitivities of IFOB test according to the size of cancers were as follows: 0% in 5 cases with a lesion less than 10 mm in size, 38% in cases with a lesion between 11 and 20 mm in size, 75% in 20 cases with a lesion between 21 and 30 mm in size. There was a statistically significant difference in sensitivity of IFOB test between the group of cancer less and more than 20 mm in size. This result suggests that IFOB test was effective in screening for colorectal cancers larger than 20 mm in size, but most of cancers smaller than 20 mm in size, even if those were advanced, had false negative IFOB tests.