SUMMARY The results from our first 43 treatments suggest the following: High malignant tumours are more sensitive to pressure treatment than low malignant types (Table VII). The situation of the tumour is of importance in so far as tumours situated close to the passage of larger vessels through the bladder wall responded poorly (Table VIII). The duration of increased intravesical pressure at values corresponding to or exceeding the diastolic (and below the systolic) blood pressure to a large extent determine the treatment result (Tables IX and X). Thus we found partial necrosis in 1 patient only who, considering the above‐mentioned factors, was treated under optimal conditions, stressing the importance of taking these factors into account when deciding upon the duration of the procedure. Hydrostatic pressure treatment is a new method and the exact definition of its indications has not yet been finalised. Patients treated up till now fall into the following groups: Extensive papillomatosis responding poorly to other treatment regimens. Recurrences, mostly isolated tumours, may occur 8–13 months after pressure treatment. These tumours are easily controlled by electrocoagulation treatment. Large isolated tumours of malignancy grade II in patients not suited for more extensive surgical interventions. Highly malignant tumours are most sensitive and this type of tumour represents in our opinion the most important indication. This is in particular true for tumours not infrequently seen close to the trigone or bladder neck. Total extirpation of the bladder and urinary diversion are in such cases the only alternative surgical treatment. Highly malignant, far advanced tumours not accessible for irradiation or surgery. The palliative improvement obtained in such cases is not without importance, considering that some of the patients lived for a further year after treatment not forgetting the influence of the procedure on pain, voiding need, hæmorrhage and urinary incontinence. In addition improved general well‐being of the patients is not infrequently seen. Hydrostatic pressure treatment may be combined with other therapeutic procedures such as irradiation. Irradiation after pressure treatment should however be delayed for 1–2 months in order not to disturb possible immunological processes. After technical failures of hydrostatic pressure treatment, the procedure may be repeated. Even following mucosal hernia, treatment may be repeated after approximately 1 week. The second treatment, however, should always be carried out by the balloon method. After muscle ruptures at least 2 months should elapse before re‐treatment. If the primary result is unsatisfactory the interval before re‐treatment may depend on the grade of malignancy of the tumour. If total necrosis of the tumour has not been achieved, low grade malignant tumours may be re‐treated already after 1 month as necrosis normally then is completed. In highly malignant tumours at least 2–3 months should elapse. We have no experience regarding pressure treatment of recurren...

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The effects of hydrostatic pressure therapy on in vitro cellular cytotoxicity responses have been studied in 19 patients with transitional cell carcinoma of the bladder (TCC). Cytotoxicity was quantitated against allogeneic targets in a microplate assay or by 51chromium isotope release. Two types of reactivity were detected, the most common being a differential cytotoxicity for targets derived from TCC, in either short-term or long-term tissue culture. This reaction is operationally termed "tumor-specific". Less frequently, a general cytotoxicity for targets of diverse histogenic origins was observed. For the present, this is termed "non-specific". Nine patients were tested before pressure therapy and of these only two gave a specific reaction and one a non-specific reaction, while six were non-reactive. Eighteen patients were tested at varying intervals after treatment and of these 11 gave a specific reaction and one a non-specific effect, while six were non-reactive. Three individuals who were non-reactive prior to therapy had a specific reaction post therapy. Two who reacted specifically before therapy became non-reactive post therapy. The results of serial in vitro testing for cytotoxicity are presented with individual case histories, tumor staging and grading and the clinical outcome of hydrostatic pressure therapy.