In this article, we reported the treatment outcomes of patients with stage I breast cancer who were enrolled in “Advanced Medicine” (NIRS ID9401) between April 2013 and November 2015. Patients not meeting eligibility criteria for the concurrently ongoing Phase I trial (UMIN ID000010848) or refusing to be enrolled in the Phase I trial were registered, so some of them were not in the low-risk breast cancer category. However, these patients were unable to receive standard treatment for physical or mental reasons, and they were accepted into “Advanced Medicine”, except for age and subtype restrictions, from the viewpoint of protecting the patients' right to receive treatment. Of these 14, three patients had comorbidities for which standard surgery was not possible, and one patient had risks with standard surgery. In the other 10 patients, surgery was possible, but their mental status made it unacceptable.
The “Advanced Medicine” program for breast cancer was abolished in March 2016, as C-ion RT for other malignant tumors was covered by national health insurance from April 2016, and the indications for "Advanced Medicine" were narrowed. A Phase II clinical trial of low-risk stage I patients (UMIN ID000010848) and a Phase I trial of stage 0 and intermediate-high risk stage I patients with C-ion RT with standard adjuvant treatment (UMIN ID 000029478) are currently in progress. Only 14 cases were analyzed in the present article because stage I breast cancers registered in "Advanced Medicine" were these 14 cases. Although other clinical trials also have registered stage I breast cancer, we believe it is appropriate to report the results of the trials individually. With a median follow-up of more than 5 years, with the exception of one high-risk recurrent case, 13 patients are alive without breast cancer and have good cosmetic outcomes.
According to MRI, the therapeutic effect of C-ion RT on primary breast tumors appeared slower than expected. As shown in Table 3 and Figure 2, the time from C-ion RT application to tumor disappearance was 3 months in 1 case, 6 months in 3 cases, 12 months in 4 cases, and 24 months in 5 cases. This result impacted the ongoing Phase I trials. In one Phase I trial, tumor resection was planned 3 months after C-ion RT to assess the pathological effects. However, this assessment 3 months after C-ion RT was then considered premature, based on the results of "Advanced Medicine" patients, and the Phase I study (UMIN ID000010848) of 7 patients was discontinued. Akamatsu et al. had reported the treatment procedure and initial course of the first case11, and the subsequent course is shown in Figure 1. In this patient, it took 24 months for tumor disappearance on MRI, but fluorodeoxyglucose (FDG) positron emission tomography (PET) showed a significant reduction in accumulation at 2 months and complete disappeared at 9 months. In all cases, both early and delayed phase enhancement of the tumor was decrease with tumor shrinkage on dynamic contrast enhanced (DCE) MRI. The accumulation on FDG PET disappeared earlier than the tumor disappearance on MR images in other patients. Assessing the activity was even more difficult by US than by MRI. Then, we recommended performing a needle biopsy on all patients to determine the efficacy of treatment, but all patients refused. The relationship between imaging results and the pathological treatment effects of C-ion RT on breast cancer requires further study. The recommended dose was set at 60.0 Gy (RBE) because no adverse reactions other than Grade 1 acute skin reactions were observed and tumor control was obtained in all cases. Therefore, we have no plans for further dose escalation.
MR images could not identify normal tissue changes within the irradiated area. This may be because the irradiated area is narrow. Breast size, shape, hardness, and nipple position compared with the untreated-side breast did not change at all in any of the cases after a 6-month period. The complete disappearance of the tumor and the absence of normal tissue changes after treatment with MRI and US were the distinguishing points from surgery and other non-surgical treatments. Other non-surgical treatment options for breast cancer usually requiring general anesthesia are associated with inflammatory pain after administration, and the tumor may remain as a mass after treatment. The only invasive procedure for C-ion RT is the insertion of alignment markers with local anesthesia, which is less invasive than other therapies. After 1 to 3 months, the tumor is softened and no longer palpable, so the patient's psychological burden is less than with other treatments. In addition, acute side effects are minimal.
Non-surgical therapies for breast cancer other than C-ion RT include radiofrequency ablation (RFA), cryoablation therapy, high-intensity focused ultrasound (HIFU) and stereotactic body radiotherapy (SBRT). Among them, the most reported is RFA. Ito et al. reported that 386 patients treated with RFA at 10 centers from 2003 to 2009 had a 5-year intra-breast recurrence-free rate of 97% for sizes ≤ 1.0 cm, 94% for 1.1 to 2.0 cm, and 87% for > 2.0 cm or more, respectively16. Nguyen et al. reviewed 30 studies, 643 cases of RFA and reported that complete ablation rates ranged from 100% to 44% with a median of 88%17. In cryoablation therapy, Lanza et al. reviewed 7 studies, 176 cases performed from 2003 to 2013, and found that complete local tumor control was 73%18. In the HIFU, She et al. reported that tumor residual rates in 6 studies for breast cancer ranged from 0 to 90%19. Regarding radical SBRT, there are even fewer reports. Shibamoto et al. reported that they performed whole breast irradiation and SBRT boost with the radiosensitizer KORTUC20 for 18 patients who refused surgery, and only one case developed local recurrence21. Barry et al. reviewed SBRT for breasts and reported that five neoadjuvant setting phase I / II trials were underway, including the ARTEMIS trial in Canada and the ABLATIVE trial in the Netherlands22. In the ABLATIVE trial, thirty-six patients were treated with neoadjuvant partial breast irradiation, and pathological complete response (pCR) was reported in 42% patients after an interval of 6 to 8 months with transient grade 2 and 3 toxicity in 31% and 3% of patients23. Compared with these treatment results, C-ion RT is presumed to have merits of high tumor control and low adverse events.
As far as we know, reports of clinical studies of C-ion RT for breast cancer are limited to our institute. Basic research has been reported from various institutes24-27, indicating that they are indeed interested in C-ion RT for breast cancer. With the growing number of C-ion RT facilities in the world, we hope that other facilities will actively research curative C-ion RT for breast cancer. Scanning and rotating gantry for respiratory movements are available at our facility, and the ongoing clinical trials use scanning irradiation to obtain better dose distribution.
At present, because of the cost of treatment and the limited number of facilities, C-ion RT for breast cancer is a limited research treatment, but research on miniaturization of device and price reduction is progressing28. We believe that clinical research of C-ion RT for breast cancer must be continued in preparation for the day when this treatment will become accessible to many patients.