The Home Run
Histotripsy and the Abscopal Effect
For some patients, Histotripsy and a stimulated immune system can elicit the Abscopal effect causing regression of many if not all of their tumors. At this time it is difficult to know which patients will undergo this response, and more data is needed on how to evaluate the response as well as maintaining the response.
Histotripsy
Histotripsy is the first non-invasive, non-ionizing and non-thermal ablation interventional radiologic technology of focused ultrasound delivered from outside the body by guided real-time imaging. Histotripsy mechanically destroys tissue through high amplitude, very short pulses that destroy tumors by creating bubbles that rupture the tumor cells, which then liquefy, while leaving normal cells undamaged. It was approved by the FDA to be marketed for clinical use in October 2023, and in November 2024 the Veterans Administration awarded a histotripsy company with a $90 million contract to develop histotripsy programs at key VA hospitals. Histotripsy was developed in the United States at the University of Michigan in the early 2000s, and has been studied on benign prostatic hyperplasia (BPH), prostate cancer, renal masses, renal calculi, blood clots, calcified aortic stenosis, fetal tumors and congenital heart diseases, uterine fibroids, bone tumors, although it has primarily been approved for liver tumors world-wide. (https://pmc.ncbi.nlm.nih.gov/articles/PMC9404673/ ; https://pubmed.ncbi.nlm.nih.gov/38639585/ )
The Abscopal Effect
The Abscopal Effect is the shrinking or disappearance of tumors in parts of the body that were not the direct target of local therapy, (which is typically radiologic intervention), as well as the regression of the target tumor lesion. It is believed that the effect is mediated by the immune system, which identifies the cancerous cells (as a result of the targeted therapy) and then attacks any of the same cancer cells wherever they are found in the body. Adding drugs called immune checkpoint inhibitors, or otherwise boosting the immune system, can enhance the abscopal effect of the immune response to cancer, although this effect cannot reliably be elicited. (https://pmc.ncbi.nlm.nih.gov/articles/PMC10116408/ ; https://www.advancesradonc.org/article/S2452-1094(22)00016-1/fulltext )
At this time there are still few facilities offering treatment attempting to elicit the Abscopal Effect, although hopefully more studies will be engineered. As of 2022, the most promising data with combined immunotherapy and radiation therapy has been found in patients with lung cancer and melanoma. There are reported studies being developed in a variety of other cancers though. (https://www.advancesradonc.org/article/S2452-1094(22)00016-1/fulltext )
To date, there are only case reports of Histotripsy and the Abscopal Effect, and not a list of clinical trials for both. (https://pmc.ncbi.nlm.nih.gov/articles/PMC7057529/ ; https://pubmed.ncbi.nlm.nih.gov/34310299/ ). There are a number of medical centers across the United States that are offering Histotripsy for liver tumors only (including metastases from primary tumors at other sites). There are also centers offering Histotripsy in China, United Arab Emirates, and KSA/ Bahrain. Medicare increased the facility reimbursement to $17,500 for histotripsy, plus there will be fees for both the radiologist and anesthesiologist (it requires a general anesthetic for liver histotripsy).
There are clinical trials underway for liver and renal tumors, as well as clinical trials on histotripsy and prostate cancer in the US, Canada and Finland, with a facility in Oregon now offering prostate histotripsy therapy. Histotripsy for brain tumors has been studied in mice, but long term effects and dosage regarding brain hemorrhage are unknown. (https://pmc.ncbi.nlm.nih.gov/articles/PMC10410615/ )
Worlikar, et al, have a promising summary of Histotripsy and potential uses for a number of different tumors as well as the medical journal articles that describe the study, results and outcomes. (https://www.tandfonline.com/doi/full/10.1080/02656736.2023.2297650#d1e358 ). These include tumors of the liver, kidney, skin, brain, pancreas, breast, prostate, thymus, blood (lymphoma) and sarcoma. As histotripsy is currently only approved for liver tumors, it further emphasizes the importance of fully knowing the true extent of cancer disease, ideally with a PET scan. We frequently have found that cancer has already metastasized when a patient finds a mass, and that the metastases will not be found on a CT scan or other blood tumor markers until it has grown significantly.
Histotripsy and the Abscopal Effect appears to be a promising non-invasive treatment option that will hopefully become readily available to all of those suffering from cancer, in addition to or in conjunction with the present treatments offered by standard of care.