Diagnostic cytology may be of use for some information in the field of cancer treatment. From the view point of morphological characteristics of cancer cells which are obtained before treatment, we can presume the prognostic courses in certain level. For example, presumption of prognosis on 420 cases with uterine cervix carcinomas according to their cytological findings before therapy (Cobalt irradiation), showed 77% in its accuracy rate. Particularly 144 cases, which were classified to FIGO Stage III were tested by cytological method, accuracy rate of prognostic presumption showed 76%. On the other hand, presumption of prognosis on same cases by means of histological method showed 68% in its accuracy rate. On the base of morphological change of cancer cells, therapeutic effects can be checked during the treatment. Reoccurrence may be recognized in early stage when any subjective or clinical symptoms manifest. Alteration of cell components, except cancer cell, shows sometimes a relation with clinical course. In pleuroperitoneal effusions, numerical alterations of macrophage and lymphocyte are valuable factors which relate to clinical course and outcome of cancer patients.