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The administration of high-energy shock waves (HESW) in clinical lithotripsy for kidney stone fragmentation is well known [1], but recent studies have revealed other potential biomedical applications for this type of acoustic energy. It has been known for a few years that HESW can be used to suppress tumor growth in vivo [2]; a temporary suppression of tumor growth for different xenografts after focal administration of HESW has been demonstrated [3]. However, the processes underlying this biological effect are poorly understood. HESW may affect tumor cells and their metabolism both directly and indirectly (for example, at the vascular level).

High-energy shock waves (HESW) can alter the growth characteristics of tumor cells in vitro, depending on the experimental set-up (Brummer et al. 1989). Furthermore, treatment with HESW can provoke suppression of tumor growth in vivo (Holmes et al. 1990; Randazzo et al. 1988; Russo et al. 1985, 1986). Our own experiments with several tumor model systems have confirmed this observation. The in vivo antitumor effect of HESW depends on the number of shock waves, the number of shock wave sessions, the initial tumor burden, and the tumor model used (Oosterhof et al. 1990). The observed tumor growth suppression in vivo is temporary and results rather in an elongated lag phase than in a permanent effect. This indicates that HESW treatment is not likely to be useful as monotherapy, and in order to obtain a longer and more definite suppression of tumor growth HESW should be combined with other treatment modalities. We therefore decided to treat the xenograft tumors with additional therapies which are known to be suboptimal. In this study we tested established tumors, known to be partially or completely insensitive to monotherapies (Beniers et al. 1988), with a combination of HEWS and either the chemotherapeutic drug doxorubicin or biological response modifier (BRM) therapy with TNFα/IFNα.