Regression of spontaneous mammary tumors in dogs after injection of neuraminidase-treated tumor cells

The effect on tumor progression produced by the injection of VCN-treated tumor cells in dogs with spontaneous mammary tumors was investigated. Untreated dogs of different races and different ages with at least two palpable spontaneous mammary tumors were selected. One of the tumors was left in the animal for further clinical examination whereas the other tumor(s) was (were) excised for preparation of a single-cell suspension by mechanical disintegration and enzymatic digestion with collagenase and trypsin. (1) In the first group, each animal was infected with 2 times 10-7 similarly prepared autologous, mitomycin-treated tumor cells; in 8 out of 12 dogs of this group the tumors progressed while so far 1 dog has died of metastasis. (2) In the second group, each animal received the same number of 2 times 10-7 tumor cells, which were mitomycin- and VCN-treated: 13 out of 15 dogs had a significant regression of their tumors to less than 10% of the original volume; in 1 dog the tumor remained unchanged and in 1 dog it progressed. (3) In the third group, 8 dogs received 1 times 10-8 mitomycin- and VCN-treated tumor cells: the application of this cell dose resulted in an accelerated tumor progression in all 8 dogs, 3 of which have already died of metastasis. The significance of these findings, with respect to potentiation and abrogation of the immunological response and with regard to immunotherapy in man, is discussed.