Effect of Methylene Blue on Tumors. ∗

Abstract

This paper deals with the results of experiments obtained with rat carcinoma-sarcoma No. 256/94 A from the Crocker Institute inoculated subcutaneously into a selected strain of rats, and with mice as described below. In the rats, the per cent of non-takes was 6.5. The spontaneous regressions, i. e., cases in which tumors were never larger than about 1 mm. in size and disappeared after a few days, were about 10%. These were not used in making computations in either set of controls or dye-treated animals. Only those tumors which reached a size larger than this and then disappeared were considered “regressions”.

Previous experiments which will be described in the full report were unsatisfactory because of the high percentage of non-takes and spontaneous regressions. This paper will deal only with a group of animals in which this difficulty has been largely eliminated.

There were 51 control animals and 87 in the treated group. Treatment, which was started when the tumor had reached a size of about 0.5 cm., consisted of daily injections into the tumor of 0.01% aqueous solution of methylene blue (Merck's medicinal). This dye was found to be the most effective of a group of oxidation-reduction indicators varying in redox-potential according to Clark's scale. The amount injected varied with the size of the tumor, which was difficult to gauge accurately, but was usually about 1/10 cc. for each mm. length of tumor; however, not more than 2 cc. was used for the large tumors to avoid possible toxic effects of the dye on the animal.

The average length of life of those animals having tumors which did not regress was 49.4 days in the controls and 45.2 in the dye treated. Those animals whose tumors regressed lived indefinitely and are therefore not included in the calculation of the above averages.