Ricerc@Sapienza

One of the most intriguing aspects of cryoablation is the potential for immune activation. In a classic example of going from the bench to the bedside and then back to the bench, the concept of the cryo-immune response is based on anecdotal reports of distant tumor regression after cryoablation of a variety of primary tumors, including breast cancer. Theoretically, in situ cryoablation is ideal for generating an anti-tumor immune response, based on the mechanism by which cryoablation kills cancer cells. Necrosis, as occurs with cryoablation, is characterized by cellular breakdown and release of intracellular contents, many of which are immunostimulatory. The immune system may also be alerted to massive cell death by factors emanating from disruption of tissue architecture, such as fibrinogen, oligosaccharides of hyaluronan, extra domain A (EDA)-containing fibronectin and heparin sulfate proteoglycan, a key component of cryo-induced cell death. Several studies have demonstrated that necrotic cells will lead to increased dendritic cell maturation and macrophage activation. In contrast to cryoablation, most other cancer therapies induce apoptosis rather than necrosis. Apoptosis involves several steps that allow the uptake of cellular debris by both macrophages and dendritic cells without release of the intracellular contents and thus without causing inflammation or an immune response. This not only does not stimulate immune recognition, but may lead to peripheral tolerance. Apoptosis leads to an inhibition of pro-inflammatory cytokines, and immunosuppressive dendritic cells that trigger clonal deletion and anergy. This concept is supported by pre-clinical studies of cryoimmunology that, across multiple animal-tumor models, demonstrated that freezing a tumor and leaving it in place could stimulate a specific anti-tumor immune response and render the animal resistant to a re-challenge. Several of these utilized murine models of breast cancer. However, not all studies of cryoablation had similar results, with some studies either failing to demonstrate a cryo-immunologic response, or documenting a negative immunologic effect of cryoablation, in some cases increasing immune suppression. Some researchers have noted that variable aspects of the cryoablation procedure may lead to either immune enhancement or immune suppression. Sabel et al., using a murine model of metastatic breast cancer, demonstrated that changing the rate of freeze, from a high rate of freeze (as is performed with breast cancer cryoablation) that causes mostly necrosis, to a low rate of freeze that results in a higher percentage of apoptosis, shifts the immune response from immunostimulatory to immunosuppressive. It is clear that greater understanding of the immunologic response to cryoablated malignant tissue is necessary to realize the full potential of breast cancer cryoablation. As part of the ACoSOG Z1072 trial, blood is being collected before and after cryoablation and after surgery to look for evidence of a cryo-induced anti-tumor immune response.
The preliminary series and the prospective phase II trial, all of which involve cryoablation followed by standard surgical resection, are obviously precursors towards the ultimate goal: cryoablation as an alternative to lumpectomy. In ACoSOG Z1072, cryoablation was effective in 92 % of targeted lesions and there was 100 % ablation in all tumors Finally, future research will be necessary to take full advantage of the immune potential of cryoablation. Although the pre-clinical data are promising, it is unclear whether any immune response generated by cryoablation would be potent enough to make a clinical impact. Eliciting the exact mechanism by which cryoablation stimulates an immune response will help shine light on ideal adjuvants to augment
that response. Already several approaches are being examined, including combining cryosurgery with systemic biological response modifiers (toll-like receptors, anti-CTLA4 monoclonal antibodies, cytokines) or intratumoral dendritic cells. Not only does the ideal adjuvant need to be identified, but the ideal timing and delivery of that adjuvant, particularly in light of breast cancer therapies such as radiation therapy or chemotherapy (which can be immunosuppressive), are all important questions for ongoing research. This could create the basis for our future clinical research studies, based on the possible choice of treating breast cancer with cryotheraphy associated with systemic biological response modifiers.