Lung carcinomas, as defined by WHO criteria, were analyzed by PAP (peroxidase-antiperoxidase) method with paraffin-embedded sections for the keratin protein. The studies consisted of 30 cases of squamous cell carcinoma (10 cases of well differentiated type, 15 cases of moderately differentiated type and 5 cases of poorly differentiated type), 3 cases of small cell carcinomaand 5 cases of adenocarcinoma.
The results were as follows:
1. The positive reaction of keratin in the lung carcinomas was the strongest in squamous cell` carcinoma among the all types.
2. The positive reaction of keratin in the squamous cell carcinoma depended upon the differentiation of tumor cells, showing stronger reaction in the perinuclear and/or pericellular area in the well differentiated type.
3. The positive reaction in the homogeneous intracytoplasmic and/or peripheral area of tumor cells was weakly noted in the adenocarcinoma.
4. The positive reaction of all three small cell carcinoma were absent. The non-neoplastic bron-
chial mucosae were :Focally and weakly observed in the bronchial and bronchiolar epithelia.
Therefore, according to the pattern of keratin positive reaction in the lung carcinomas, it was
suggested that well differentiated squamous cell carcinoma contained abundant keratin, whereas
poorly differentiated squamous cell carcinoma and adenocarcinoma contained less amounts.
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