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Introduction

Symptoms such as bleeding and tissue breakdown due to progression of locally advanced breast cancer (LABC) and locally recurrent breast cancer (LRBC) are events that lead to a reduction in quality of life (QOL), and it is often difficult to deal with them because the symptoms cannot be alleviated at the terminal stage. Surgical treatment is difficult for advanced lesions that cannot be controlled by radiation therapy (RT). If RT enables local control, the patient's QOL will improve. However, LABC and LRBC are often situations in which drug therapy is ineffective, and it is difficult to obtain local control with RT alone, because such lesions contain numerous hypoxic cancer cells and antioxidant enzymes that may confer resistance to RT (1-3).

As reported in past studies (1-5), a novel radiosensitizer, Kochi Oxydol Radiation Therapy for Unresectable Carcinomas II (KORTUC II), was developed for the treatment of cancers that contain numerous hypoxic cancer cells and antioxidant enzymes. Following KORTUC II therapy, hypoxic and radioresistant cancer cells become hyperoxic and radiosensitive. The concept of KORTUC II is to transform radioresistant cancer into radiosensitive cancer (1-6). KORTUC II was first used in Kochi University in 2006 and is currently the most widely used radiosensitizer in clinical practice in Japan. Our institution has used KORTUC (I+II) in over 250 patients to date since the first patient was treated in May 2010 after obtaining approval from the University's Ethics Committee. (KORTUC I involves application of the sensitizer to neoplastic surface tissue rather than injecting the sensitizer into tumor tissue.) KORTUC II has achieved significant local effects with no notable adverse events. In this article, we report on the cases where KORTUC II was used to treat patients with LABC or LRBC.

Subjects and methods

Patient selection

At our institution, KORTUC II treatment was performed after detailed informed consent given in written form was obtained from patients who were expected to survive at least a year and met the following additional criteria: i) Local control by conventional radiotherapy alone was presumed to be difficult; ii) the dosage of additional irradiation they could receive was limited; and iii) they refused surgery as a treatment option. Hormone therapy or systemic chemotherapy was used concomitantly in some patients according to the judgment of the attending breast surgeon and the patient's wishes. KORTUC II treatment was approved by Osaka Medical College Clinical Trials Registry, trial no. 1973, (May 10, 2010) and UMIN Clinical Trials Registry, trial no. UMIN000003734, (June 10, 2010).

Of the 37 patients treated with KORTUC II for LABC or LRBC between February 2011 and January 2020, the 30 patients who were followed up for at least 3 months after treatment were included in the study. These subjects consisted of 9 patients with LABC (1 in stage IIIA, 5 in stage IIIB, and 3 in stage IV) and 21 patients with LRBC.

Radiotherapy

RT was performed for the purpose of local control with external beam irradiation (X-ray or electron beam) to locally advanced lesions, recurrent lesions or metastatic lesions of the breast, chest wall, axillary lymph nodes, and supraclavicular fossa lymph nodes. The dose and extent, as well as particular tumor sites to be irradiated, were determined by the attending physicians considering factors including tumor size and location, concomitant therapies, presence/absence of metastases outside the irradiation fields, and general condition of the patient.

In principle, the irradiation fields were to include all lesions for stage III LABC, and local areas that required local control for stage IV LABC and LRBC patients.

Dosing method of the sensitizer

This sensitizer is a solution consisting of 0.83% sodium hyaluronate and 0.5% hydrogen peroxide (H2O2, also known as ‘oxydol’ in Japan) by volume. It is prepared aseptically before each use by adding 2.5 ml of sodium hyaluronate (Adant® Dispo) and 1 ml of 1% xylocaine to 0.5 ml of oxydol and mixing them to be dispensed as a total volume of 4 ml from a single vial. Our standard dosing protocol called for 1 vial for tumors <3 cm in diameter, 2 vials for tumors 3-<5 cm in diameter, ≥3 vials for tumors ≥5 cm in diameter, with a maximum dose of 5 vials for giant tumors. However, the optimal dose is still uncertain.

The sensitizer was injected into the tumor twice weekly immediately before RT either under direct vision in the case of tumors close to the skin, or under ultrasound or CT guidance. Under ultrasound guidance, when the sensitizer is injected into a tumor, oxygen is generated in the form of micro-bubbles and the tumor can immediately be recognized as a high echo area. The sensitizer was injected so that oxygen was distributed in the entire tumor. Usually, injections of the sensitizer occurred after the patient had already received approximately 20 Gy at the beginning of a course of RT. This was to prevent the increased intra-tumor pressure from the injections causing viable tumor cells to infiltrate into nearby lymphatic and blood vessels (5). To prevent dissemination along the injection route, punctures were made on the skin surface in the irradiation field, whenever possible.

Items examined

To examine the local effects, the tumor size was measured before treatment and at the estimated time of greatest regression (smallest volume) within 2 years after treatment. From this, the maximum tumor shrinkage (MTS) was calculated according to the percent decrease in tumor volume revealed by CT imaging at the estimated time of greatest regression. The tumor volume was measured based on CT images using the Eclipse radiation treatment planning system (Varian Medical Systems, Inc.). This interval to greatest regression was determined based upon prior studies using contrast-enhanced MRI that show, on average, 14 months are required between KORTUC II therapy and tumor disappearance according to RESIST criteria. However, there is no pre-determined protocol for scheduling follow-up imaging tests. In particular, CT scans to evaluate treatment effects were performed in a timely manner depending on the situations of individual cases. In addition to the CT-determined volume measurements, MRI, and PET-CT imaging were conducted when deemed appropriate to assess the presence and extent of any residual tumor in the treated area. The duration of loco-regional control (LC) was determined by the time in months at which tumor regrowth in the irradiated target lesion was noted by one of these imaging techniques, and this event indicated local recurrence. LC and duration of progression free survival (PFS) after the completion of RT were determined using the Kaplan-Meier method. In the case of LC and PFS, death of the subject was regarded a censoring event.

The irradiation dose was calculated as equivalents of 2 Gy fractions (EQD2) with the α/β ratio of 3.5 (breast cancer has a low ratio of α/β), and described as Gy3.5 (7,8). Additionally, the subjects were divided into two groups, less than 60 Gy3.5 (60 Gy<) and 60 Gy3.5 or more (≥60 Gy), and evaluated according to whether there was a statistically significant difference in number of sensitizer injections, MTS, duration of LC, and time to progression (TTP) using Student's t-test. Comparison of duration of LC and PFS between the two groups (60 Gy<, ≥60 Gy) was evaluated using the Kaplan-Meier method.

Statistical analysis

Survival periods were measured starting from the day after end of treatment. The tumor volume was measured by the radiotherapy planning device Varian (Varian Medical 85 Systems) Eclipse ver.11.0. Continuous variables are presented as mean ± standard deviation. Categorical variables are presented as numbers (percentage). The Kaplan-Meier method was used to calculate survival analysis and the differences were compared using Wilcoxon rank sum test. Comparison between the 2 groups, differences in parameters depending on the irradiation dose filled was performed using the Wilcoxon rank sum test. All experiments were performed in duplicate. For analyses, EZR software, version 1.54 and statistical data analysis in Excel 2016 was used. P<0.05 was considered to indicate statistically significant differences.

Results

Patients treated with KORTUC II

Table I shows the baseline patient characteristics. All of the 30 patients were women, and the mean age was 61 years (43-75 years). RT was performed at the median dose of 53 Gy/19 Fr (40 Gy/16 Fr-67.5 Gy/25 F). The median irradiation dose was 60.4 Gy3.5 (43.6-76.1 Gy3.5). The median total number of sensitizer injections was 5 (2-7). Of the 30 patients, 22 patients were treated concomitantly with hormone therapy and 18 patients with chemotherapy. Concomitant treatment status for one patient was unknown. The median follow-up period was 19 months (3-106 months).

Table I Patient characteristics.

Table I

Patient characteristics.

Patient no.	Age, years	Disease	Stage	Irradiation site	Radiation dose, Gy	Number of fraction	EQD2 Gy3.5	Number of sensitizer injections	Hormonal therapy	Chemotherapy
1	45	LRBC		CW	44	18	48	4	-	-
2	75	LRBC		CW	40	16	44	7	-	+
3	70	LABC	IIIB	CW, Ax	67	25	77	6	+	+
4	57	LABC	IV	CW, Ax	59	21	69	7	+	+
5	67	LRBC		CW	53	19	61	5	+	+
6	54	LRBC		Br, Ax	59	21	69	3	+	+
7	56	LRBC		CW	53	21	59	6	UK	UK
8	60	LRBC		Br	59	22	68	6	-	-
9	67	LRBC		CW, Ax	58	25	62	6	+	+
10	49	LRBC		Br	58	29	59	5	+	+
11	68	LRBC		Br, Ax	54	18	65	5	+	-
12	75	LRBC		Br	59	21	69	5	+	-
13	58	LRBC		CW	59	21	69	5	+	+
14	73	LRBC		CW	59	21	69	5	+	-
15	75	LRBC		Br	59	21	69	4	+	+
16	67	LRBC		CW, Ax, SC	60	30	60	3	+	-
17	59	LRBC		Ax, SC	60	30	60	5	+	+
18	72	LABC	IV	CW	44	16	51	3	+	+
19	51	LRBC		SC, Neck	60	30	60	2	-	+
20	74	LRBC		Br, Ax	53	19	61	5	+	+
21	74	LABC	IIIB	Br, Ax, SC	53	19	61	5	+	-
22	52	LRBC		CW	40	16	44	3	+	+
23	43	LRBC		CW	53	19	61	5	-	+
24	58	LRBC		Br	53	19	61	5	+	+
25	61	LRBC		CW	44	16	51	3	+	+
26	43	LABC	IIIA	Br, Ax, SC	53	19	61	5	-	+
27	48	LABC	IV	Br, Ax, SC	53	19	61	5	+	-
28	59	LABC	IIIB	Br, Ax	53	19	61	5	+	-
29	52	LABC	IIIB	Br, Ax, SC	53	19	61	5	-	-
30	70	LABC	IIIB	Br, Ax, SC	53	19	61	5	+	-

[i] LRBC has no description of staging due to recurrence status. LABC, local advanced breast cancer; LRBC, local recurrence breast cancer; Br, breast; CW, chest wall; Ax, axilla; SC, supraclavicular fossa; UK, unknown; EQD2 Gy3.5, equivalent dose in 2 Gy fractions with the α/β ratio of 3.5.

Tumor shrinkage rate by KORTUC II

Table II shows the therapeutic effects. The median baseline breast cancer tumor volume measured using CT, was 53.2 cm3 and the mean volume was 116.5 cm3 (4.2-642.5 cm3). Following KORTUC II therapy, the median MTS was 97.0% (standard deviation=9.8%) and the mean was 91.7% (range 77.2-100%). Fifteen patients (50%) were assessed to have achieved a clinical complete response (cCR) as a temporary effect. The median evaluation period until MTS was 8 months (2-17 months).

Table II Treatment effects.

Table II

Treatment effects.

Patient No.	Pre-TTV, cm3	MTS, %	Temporary effect	Time to MTS, months	Regrowth in field	LC, months	Regrowth out of field	TTP, months	Follow up, months	Prognosis
1	27.3	82.1	cPR	15	-	36	+	15	36	AWD
2	32.4	100.0	cCR	6	-	88	+	21	88	AWD
3	220.3	100.0	cCR	8	+	30	+	20	35	DOD
4	397.8	94.1	cPR	12	-	35	+	21	45	AWD
5	4.2	100.0	cCR	3	+	36	+	20	106	AWD
6	240.5	100.0	cCR	3	-	6	+	3	6	DOD
7	25.9	100.0	cCR	3	-	3	-	3	3	NED
8	446.0	77.0	cPR	2	-	3	-	3	3	AWD
9	179.6	86.4	cPR	12	+	37	+	37	46	DOD
10	26.9	88.1	cPR	13	-	28	+	6	28	DOD
11	642.5	100.0	cCR	8	-	21	+	4	21	AWD
12	71.9	100.0	cCR	17	-	28	-	28	28	DOAD (pancreatic cancer)
13	176.9	78.7	cCR	10	-	72	+	4	72	AWD
14	25.3	100.0	cCR	5	-	33	-	33	33	NED
15	39.0	100.0	cCR	8	-	13	+	13	13	DOD
16	4.2	100.0	cCR	17	-	62	-	62	62	NED
17	29.5	100.0	cCR	9	-	59	+	11	59	AWD
18	260.1	84.5	cPR	12	-	37	+	4	37	AWD
19	68.2	90.8	cPR	5	-	8	+	1	8	DOD
20	65.6	76.1	cPR	12	-	25	+	5	25	AWD
21	23.7	100.0	cCR	16	-	16	-	16	16	NED
22	116.7	74.7	cPR	7	-	17	+	9	17	AWD
23	5.4	72.2	cPR	3	+	12	+	2	14	DOD
24	20.3	100.0	cCR	9	-	9	-	9	9	DOD
25	113.5	73.1	cPR	1	-	3	+	1	3	AWD
26	35.7	100.0	cCR	7	-	7	-	7	7	NED
27	7.2	100.0	cCR	5	-	11	-	11	11	NED
28	26.2	89.3	cPR	6	-	9	-	9	9	AWD
29	83.2	92.5	cPR	4	-	7	-	7	7	AWD
30	78.1	91.4	cPR	5	-	7	-	7	7	AWD

[i] Pre-TTV, pre-treatment tumor volume; MTS, maximum tumor shrinkage; LC, local control; TTP, time to progression; cCR, clinical complete response; cPR, clinical partial response; NED, no evidence of disease; AWD, alive with disease; DOD, death of disease; DOAD, death of another disease.

Loco-regional control and progression free survival

Tumor regrowth in treated lesions occurred in 4 patients (13.3%) at 30, 37, 36, and 12 months after treatment. The proportion of patients with enduring LC at 1, 2, and 3 years was 100, 94.7, and 75.4%, respectively, as shown in the Kaplan-Meier curve (Fig. 1). Seventeen patients (56.7%) presented with tumor exacerbation outside the irradiation field. The median duration of PFS was 9 months (2-62 months). Nine patients (30%) died-eight of the primary disease, and one of other disease (pancreatic cancer). The proportion of patients with PFS after RT at 1 and 2 years was 59.0, and 24.1%, respectively, as shown in Fig. 2. Two patients (nos. 6 and 23) developed chest wall necrosis in the irradiated area 2 and 3 months after RT, respectively.

Figure 1 Kaplan-Meier curve of LC. The LC rates were 100, 94.7 and 75.4% at 1, 2 and 3 years, respectively. LC, loco-regional control.

Figure 2 Kaplan-Meier curve of PFS after the completion of radiation therapy. The proportions with PFS were 59 and 24% of the 30 subjects at 1 and 2 years, respectively. PFS, progression free survival.

Subgroup analysis between 60 Gy< and ≥60 Gy

Table III shows that the difference in the calculated EQD2 between the two groups, 60 Gy< and ≥60 Gy, was statistically significant (P<0.01). On the other hand, there was no significant difference in number of sensitizer injections (P=0.40), MTS (P=0.09), duration of LC (P=0.49), and TTP (P=0.30). There was no difference in duration of LC (P=0.19) and PFS (P=0.21) between the two groups, as shown in Figs. 3 and 4.

Figure 3 Kaplan-Meier curve of LC (<60 and ≥60 Gy). Wilcoxon P=0.19. There was no difference in duration of LC between the two groups (<60 and ≥60 Gy). LC, loco-regional control.

Figure 4 Kaplan-Meier curve of PFS (<60 and ≥60 Gy). Wilcoxon P=0.21. There was no difference in duration of PFS between the two groups (<60 and ≥60 Gy). PFS, progression free survival.

Table III Differences in selected parameters according to radiation dose (Wilcoxon rank sum test).

Table III

Differences in selected parameters according to radiation dose (Wilcoxon rank sum test).

Outcome	<60 Gy	≥60 Gy	P-value
Number of patients (%)	7 (23%)	23 (77%)
EQD2(3.5), avg. Gy	50.2	63.5	<0.01
Total number of injections, avg.	4.4	4.9	0.40
MTS, avg. %	86.1	93.4	0.09
Duration of LC, avg. months	30.3	23.7	0.49
TTP, avg. months	8.4	14.5	0.30

[i] There was no significant difference in total number of sensitizer injections, MTS, duration of LC and TTP. avg., average; EQD2(3.5), equivalent dose in 2 Gy fractions with the α/β ratio of 3.5; MTS, maximum tumor shrinkage; LC, local control; TTP, time to progression.

Discussion

Radiosensitizers have been widely studied as a method to enhance the effects of RT. Although a number of radiosensitizers, including misonidazole, were developed in the past (9-12), many of them have not been used in clinical settings due to adverse reactions such as peripheral neuropathy. In this context, KORTUC II, a new enzyme-targeting and radiation sensitizer developed at Kochi University, has gathered attention (1-6). The sensitizer contains H2O2 and hyaluronic acid as its main components, which, along with their decomposition products, are harmless to the human body. This suggests it is a safe sensitizer if proper dosage is used and attention is paid to avoid procedural problems such as incorrect administration into blood vessels (5). The severity of acute-phase adverse events, such as radio-dermatitis, has been reported to be comparable with that following adjuvant radiation for regular breast-conserving therapy (13-15). Also, no particular delay in acute-phase injuries has been observed. At our institution, we have used KORTUC II to treat over 250 cases of various solid cancers, including the LABC and LRBC reported in this article, but have observed no marked adverse reactions.

In our study, the 30 patients who underwent KORTUC II treatment experienced median MTS of 97%, the cCR rate was 50%, and the LC rate was 100, 94.7, and 75.4% at 1, 2, and 3 years, respectively (median follow-up period 19 months). Generally, excellent LC was obtained after therapy. Patients with LABC and LRBC have the potential for long term survival, and treatment that provides continuous symptom relief and local control is desired. The standard treatment for LABC is multidisciplinary treatment, with chemotherapy followed by local therapy such as surgery and RT (16-18). Twenty one of the 30 patients who received KORTUC treatment (70%) experienced tumor re-growth, despite all having received chemo or hormonal therapy. Even in these cases, tumor shrinkage was also observed and QOL was improved.

Regarding the radiation dose, it has been reported that irradiation of 30 Gy or more had a significant effect on symptom relief, and that patients who received 60 Gy or more at the primary site had a higher local control rate for 5 years compared with patients who received less than 60 Gy (19,20). Sheldon et al (19) concluded that high-dose RT without mastectomy is an effective means of local control of LABC. In our case, we administered a high dose with a median 60.4 Gy3.5, but at this relatively high dose level there was no statistically significant difference in MTS, duration of LC and TTP depending on the irradiation dose. Although the responses of these 30 patients seems favorable considering their pre-treatment conditions, because individualized multidisciplinary treatment is used for LABC and LRBC, it would be difficult to compare the responses with those of patients who did not receive KORTUC II. Future well controlled cohort or retrospective case-control studies are necessary to address this issue.

Takaoka et al (21) reported the in vivo efficacy of radiotherapy combined with prior intratumoral H2O2 injection. A dose-modifying factor of 1.3-1.5 would be expected when combined with fractionated radiotherapy. If 3% H2O2 were injected alone, it would cause severe pain at the injection site. However, diluting the sensitizer fivefold with sodium hyaluronate reduces this pain to a mild level in the experience of our institution. In addition, mixing the moderately viscous sodium hyaluronate with the sensitizer retards its enzymatic breakdown and dispersion, resulting in an elevated oxygen partial pressure inside the tumor for over 24 h (3,4,6,22). Therefore, twice-weekly intra-tumor local injection may be the best regimen, considering the sensitizing effects, need to limit patient discomfort, and the effort of injection. Another major advantage is that H2O2 and sodium hyaluronate are inexpensive agents.

In addition, sodium hyaluronate itself may have the potential to suppress cancer progression and metastasis (23-26). It has highly metabolized in the lymphatic system, and migrates readily via lymphatic capillaries to regional lymph nodes following injection into breast tumor tissue (27-29). When accompanied by H2O2, these two compounds together can sensitize metastatic foci in lymph nodes. In the cases of KORTUC II treatment for first-episode breast cancer in our institution, we have experienced many cases of regression of axillary and supraclavicular fossa lymph node metastases in patients who received local injections of the sensitizer into the primary tumor, although none was injected into the metastatic nodes. CD44, which is highly expressed on the surface of cancer stem cells, is an adhesion molecule for which hyaluronic acid is a ligand (26,30,31). This sensitizer is believed to target even the breast cancer stem cells (14).

Generally, KORTUC II aimed for local tumor control and symptom relief in patients with LABC and LRBC. Patients with unresectable LABC and LRBC often have severely compromised QOL, due to massive exudation and bleeding from the lesion, odor, and disfigurement. NCCN guidelines version 5. 2020(32) recommends multidisciplinary treatment for LABC with a focus on drug therapy supplemented by surgery and RT. However, in many cases, regular RT fails to achieve satisfactory results for patients with unresectable tumors and many of these patients also do not respond to drug therapy. In this study, we have achieved significant local effects in the treatment of LABC and LRBC with a diameter of 10 cm or larger and open skin lesions. KORTUC II has improved greatly QOL and has been appreciated by the patients who received this therapy (15), suggesting it is a highly satisfactory treatment option.

Although the KORTUC II is effective in LC, it requires precautions, as soft tissue necrosis of the chest wall was observed in two patients after treatment. Their common features were that the tumor had invaded deep into the chest wall and the soft tissue necrosis occurred at the same time as the malignant lesions were expanding. The soft tissue necrosis may have been caused by inhibition of normal tissue recovery together with tumor tissue necrosis. Therefore, if imaging shows the tumor is invading deep into the chest wall and the tumor is growing rapidly, it may be best to forego or limit KORTUC II therapy to reduce the risk of soft tissue necrosis. It should be noted that soft tissue necrosis of the chest wall has also been reported with RT alone (33).

Many fundamental issues remain to be clarified related to KORTUC II, particularly quantified levels of patient benefit and how KORTUC II can be combined optimally with radiation, chemotherapy and immunotherapy to treat various cancers. To date only a single phase 1 clinical trial has been completed, and this showed no significant adverse effects in patients with LABC (34). Nimalasena et al (34) reported that injection pain was tolerable, dermatitis was not exacerbated, and the tumor regression rate was 50-100%. Biomarker tests demonstrated significant changes in IL-4, MIP-1α, IL-1β, and TRAIL compared with those of the patient group without sensitizer, suggesting apoptosis induced by TNF-related apoptosis-inducing ligands associated with activated T-cell signaling and increased macrophage stimulation (34). Kariya et al (35) reported that H2O2 enhanced lysosome-dependent X-ray-induced apoptosis in an in vitro experiment. A phase 2 study has been underway in five sites in the United Kingdom since June 2020-the only phase 2 trial to date. In the future, we need more clinical trials to promote widespread use of KORTUC II and to include it within insurance coverage.

In conclusion, KORTUC II demonstrated high rates of LC for LABC and LRBC. These effects may not be achievable with regular RT alone. Moreover, this method can play a major role in alleviating symptoms. KORTUC II is expected to be an inexpensive and extremely promising mode of RT with an excellent radiosensitizing effect.

Acknowledgements

The authors would like to thank Dr Yasuhiro Ogawa (Department of Radiation Oncology, Kochi General Rehabilitation Hospital, Kochi, Japan), visionary inventor of the KORTUC.

Funding

No funding was received.

Availability of data and materials

The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

Authors' contributions

TS and KN designed the study and wrote the manuscript. TS, YU and HA analyzed and interpreted the patient's clinical data for the manuscript. TS, MN, HY, CS, AH, KK and MI performed the KORTUC treatment and statistical analysis. KY contributed to collecting the relevant literature and to data analysis, and reviewed and critically interpreted the information. TS and HY confirm the authenticity of all the raw data. All authors have read and approved the final manuscript.

Ethics approval and consent to participate

Written informed consent was obtained from all patients. Approval was obtained from the Ethics Committee of Osaka Medical College (Osaka, Japan), trial no. 1973 (May 10, 2010).

Patient consent for publication

The patients provided written informed consent for the publication.

Competing interests

The authors declare that they have no competing interests.

References