Adaptation to the tumor-enhancing effects of stress.

Growth of P815 mastocytoma in syngeneic DBA/2J male mice was evaluated following several stress regimens. Although escapable shock did not enhance tumor growth, an equivalent amount of inescapable shock applied in a yoked paradigm markedly augmented tumor development. If mice received repeated stress sessions on 5-10 consecutive following tumor cell transplantation, the tumor-enhancing effects of an acute session were abrogated. This effect was not due to an antitumor effect exerted by a shock session applied several days after cell transplantation. It seems that the tumorigenic effects of stress are subject to adaptation since stress exposure prior to cell transplantation also inhibited the effects of an acute stress session. The data were discussed in relation to stress-induced neurochemical alterations.