Breast cancer is not currently approved as a treatment in any location, but is in clinical trials in the US and Canada.
In 2007, approximately 178,000 women were informed by their doctor that they had invasive breast cancer and 62,000 were told that they had the in situ breast cancer. Over 40,000 died. These stark figures underscore the limitations of the therapies we have at our disposal to treat this disease. Most breast cancer patients undergo treatment that includes painful and disfiguring surgery, often combined with exhausting courses of radiotherapy and chemotherapy, yet all too many succumb to the disease.
A Noninvasive Alternative
MR-guided focused ultrasound—based on two groundbreaking core technologies—has the potential to revolutionize the treatment of breast cancer. MR-guided focused ultrasound will likely give physicians the ability to destroy tumors by producing precise amounts of heat and vibration within the body with pinpoint accuracy. And because it uses heat rather than radiation to destroy tissue, it can be used again and again without harmful side effects. When fully tested, MR-guided focused ultrasound surgery could offer women a highly effective, noninvasive alternative to destructive surgery, with much less pain, much shorter recovery, and fewer emotional consequences.Targeted High-Potency Chemotherapy
The last great life-saving advance in breast cancer treatment was the introduction of chemotherapy drugs like tamoxifen and herceptin. MR-guided focused ultrasound could dramatically increase the efficacy of these treatments by providing a delivery system that releases pharmaceuticals directly to a tumor site. Physicians could deliver these chemotherapy agents in much higher concentrations and lower doses without the systemic toxicity associated with current methods.
How Focused Ultrasound Could Become the Prefered Treatment Option
Breast tumors can often be fast-growing tumors that spread into the surrounding areas and are likely to become malignant. Ultrasound treatment guided by imaging in the treatment of breast cancer presents some interesting challenges in this application. The important challenges for treating breast tumors include killing all the tumor cells, getting a clear margin around the tumor, and checking the lymph nodes for tumor tissue to see if the tumor has started to metastasize (travel through the circulatory system to other parts of the body). Clear margin refers to the practice of taking approximately 10 mm of good tissue all the way around the tumor to ensure that all the tumors tissue is killed or removed.
New research has identified tumor types by surface antigens (protein molecules in the cell membranes). Drugs, like tamoxifen, have been developed to target specific types of tumors (estrogen rich). To date there is no research on using with MR guided focused ultrasound on different types of tumors. Like in uterine fibroids, some types of tumors may be more tissue dense and require more energy to kill the cells by thermal ablation.
Other variables that may affect the use of focused ultrasound treatments may include tumor size (<2 cm, 2-5 cm, > 5 cm). Larger tumors may require more heat energy and longer treatment times than are practical. A good understanding of what can be achieved realistically is necessary to ensure that treatment attains 100% ablation of the tumor.
Additionally, some tumors show evidence of branching through the mammary ducts, called ductal carcinoma in situ (DCIS). In order for MR guided focused ultrasound to be effective, the imaging technique must accurately delineate all parts of the tumor, even in the mammary ducts, so that even this branching component is treated with ablation.
One currently known limitation of MR guided focused ultrasound is that the tumor must be more than one cm away from the skin surface to prevent skin burns.
Areas currently under investigation include:
- Ensuring that all the tumor tissue is 100% ablated – studies to date have noted some variability which may be related to size or type of tumor
- Small tumors < 2cm show 100% ablation whereas larger tumors > 5cm have shown that 100% ablation was not achieved all the time
- Lack of complete ablation could be related to size or tissue type and has not been studied intensively yet
- Size could be due to a time component of the treatment of large tumors, or non-overlapping sonications, or tissue/patient movement during treatment
- Tumor type could be related to tissue density and the amount of energy needed for thermal ablation to be successful
- Ensuring that good margins around the tumor (10 mm healthy tissue) are attained – accurate tumor volume determination is critical
- In the presence of DCIS, MR is the most reliable imaging technique, but it may over- or underestimate tumor size
- Techniques for margin assessment and residual tumor detection after ablation need to be developed; histopathological assessment of lymph nodes is contrary to the purpose of non-invasive techniques, but is an important prognostic factor to estimate favorable or unfavorable outcomes
- Sentinel lymph node biopsy could be an alternative – needs testing to determine reliability of the test
As new drugs like tamoxifen come to market and can be used to shrink the tumors, MR guided focused ultrasound could be a paired with chemotherapy before treatment and could be a means whereby targeted drug delivery could be used before or after treatment. Additionally, imaging techniques are being developed to differentiate good tissue from tumor tissue better. Transducers and anatomical positioning aids may improve the reach, minimize the distance tumor-to-skin and minimize patient movement during treatment. As all these areas under investigation come together and are optimized, it is hoped that focused ultrasound will become a preferred treatment option. In the meantime, clinical trials are needed to test these innovations in treatment.