Preface

The Japanese Breast Cancer Society (JBCS) initiated a breast cancer registry in 1975. In 2004, this registry transitioned to a web-based system in collaboration with the non-profit organization Japan Clinical Research Support Unit and the Public Health Research Foundation, Tokyo, Japan. In 2012, the National Clinical Database (NCD) took over the management of this registry. Further details of this system have been outlined in a prior publication [1]. Facilities across Japan participating in the NCD register patients diagnosed with new-onset breast cancer (BC). Since the inception of its current platform, the National Clinical Database-Breast Cancer Registry (NCD-BCR), in 2012, the registry has documented 945,398 BC cases through 2019 [2, 3].

Utilizing NCD-BCR data, institutions can obtain certification for surgical specialty training programs, and surgeons can either acquire or renew their professional licenses. The data has also been the basis for numerous retrospective observational studies [4,5,6,7,8,9,10,11,12,13,14,15,16,17]. Together, the JBCS and NCD Office aim to improve quality of medical care by relaying quality indicator data to BC treatment providers.

Japan has the most aged population in the world. In 2020, the Japanese Ministry of Health, Labour and Welfare reported that life expectancy was 24.8 years for 65-year-old women and 16.1 years for 75-year-old women. Therefore, it is important to evaluate the prognosis for elderly patients with BC in Japan when determining the most appropriate treatment approach.

This annual NCD-BCR report presents an overview of 93,784 BC cases registered in 2020 from 1364 institutes. Additionally, we provide an analysis of 10-year mortality rates for 36,279 elderly patients, over 65 years of age, who underwent surgery for Stage I-III BC between 2008 and 2012.

Demographics and patients’ characteristics

Of 93,784 BC cases, 93,193 (99.4%) were female. The median age at cancer diagnosis was 61 years with an interquartile range from 49 to 72 years. Moreover, 44% (41,149 patients) were aged over 65 (Table 1). The distribution of surgical procedures across various regions in Japan for female patients is as follows: 4.4% in Hokkaido, 6.4% in Tohoku, 35.0% in Kanto, 15.8% in Chubu, 5.7% in Chugoku, 3.1% in Shikoku, and 11.6% in Kyushu/Okinawa. Synchronous bilateral BC was observed in 6262 cases (6.7%), and a family history of BC was noted in 16,052 cases (17.2%). Regarding clinical Stage, 57.5% (53,531) of the female patients were diagnosed with early-stage BC of Stage 0 or I.

Table 1 Characteristics of breast cancer patients registered in 2020
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Pathology

The pathological assessment of surgical specimens for 89,783 patients with BC regardless of preoperative therapy revealed that 10,480 (11.7%) were finally diagnosed as pTis. The most frequent range of invasive tumor size was from 1.1 to 2.0 cm (26,899 patients, 30.0%). Of the 81,549 patients who received surgery on axillary lymph nodes, 77.3% had no axillary lymph node metastasis (pN0), while 6.1% (4952 patients) had metastasis in more than four axillary nodes. Of the 89,853 patients who received breast surgery, 75.1% were ER (estrogen receptor) positive (more than 10% positive cells), 62.1% were PgR (progesterone receptor) positive, and 14.3% were HER2 (Human Epidermal Growth Factor Receptor 2) positive. Out of the 75,370 cases where Ki67 was measured after the breast surgery, 24.8% (22,316 patients) exhibited a Ki67 positivity rate of more than 30%.

Breast cancer treatment

The types of surgeries categorized by cStage are presented in Table 2. Out of the 92,649 patients who underwent surgery, 39,875 (43.0%) had a partial mastectomy. The rates of breast-conserving surgery were 58.5% for cStage I, 30.8% for cStage II, and 13.1% for cStage III. A total of 68,156 patients (73.6%) underwent a sentinel lymph node biopsy (SLNB), and among them, 7164 (7.7%) subsequently had axillary node dissection. Among 48,040 patients without distant metastasis who received mastectomy, a total of 5563 (11.6%) patients underwent breast reconstruction procedures (Table 3).

Table 2 Surgical procedure according to cStage
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Table 3 Procedure of reconstructive surgery among patients without distant metastasis
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The number of patients without distant metastasis who underwent postoperative radiotherapy is outlined in Table 4. Among the 39,216 patients who had breast-conserving surgery, 27,457 (70.0%) received whole breast irradiation, while 2080 (5.3%) were treated with radiotherapy to both the whole breast and regional lymph nodes. Of the 48,411 patients who had a mastectomy, 4808 (9.9%) received radiotherapy to the chest wall and regional lymph nodes, and 588 (1.2%) received radiotherapy only to the chest wall.

Table 4 Radiotherapy after breast surgery for patients without distant metastasis
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The types of systemic therapies administered either before or after surgery to patients without distant metastasis are detailed in Table 5. Of the 89,853 patients who underwent surgery, 10,773 (12.0%) were given neoadjuvant chemotherapy. Post-surgery, 18,971 patients (21.1%) received chemotherapy, and 56,365 (62.7%) were treated with endocrine therapy.

Table 5 Types of systemic treatment in the pre- or post-operative therapies for patients without metastasis
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Ten-year mortality of elderly patients after surgery for breast cancer

In addition to presenting the characteristics of breast cancer patients registered in 2020, we conducted an analysis of the ten-year mortality rates for elderly BC patients diagnosed between 2008 and 2012. This analysis focused on patients with available clinical data, including age, ER, PgR, and HER2 status (Supplement figure). We utilized cStage information for patients who underwent neoadjuvant therapy and pStage information for those who did not. The BC subtypes were categorized as follows: luminal-type (ER or PgR positive with over 10% cell positivity), HER2-type (HER2 positive with any ER/PgR status), and triple-negative (ER and PgR negative with HER2 negative status). Patients with synchronous or metachronous bilateral BC were excluded from the analysis.

In Fig. 1 and supplementary tables, we present the ten-year mortality rates of elderly BC patients stratified by Stage, subtype, and age. In all stages and subtypes, 10-year mortality rates increased with age. For Stage I BC, it is noteworthy that the incidence of deaths due to non-breast cancer-related causes surpassed that of breast cancer-related deaths among individuals aged 65 and older, regardless of subtype. In HER2-type and triple-negative BC, there was a progressive increase in the likelihood of death due to BC as age advanced. In Stage II BC, patients aged 70 years or older with luminal-type BC were likely to die from causes other than BC. In contrast, patients under 80 years old with HER2-type and triple-negative BC tended to have a higher rate of death from BC compared to other causes. In Stage III, the risk of breast cancer-related mortality was notably elevated, surpassing the risk of death from other causes especially for HER2 and triple-negative BC in most age groups.

Fig. 1
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Ten-year mortality among elderly patients who received a surgery for breast cancer (BC) diagnosed between 2008 and 2012

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Our study reveals distinct mortality patterns by stage and subtype in elderly breast cancer patients and underscores the need for personalized treatment strategies that consider subtype-specific aggressiveness and age-related health factors. As elderly populations continue to grow, healthcare systems must adapt to meet the evolving needs of elderly breast cancer patients, aiming for optimal outcomes and quality of life.

Postscript

The detailed data regarding the treatment for BC, available within the Japanese Breast Cancer Registry, is a result of voluntary contributions by healthcare professionals, including physicians, across Japan. We sincerely acknowledge and appreciate their dedication in inputting this information. It is through their collective efforts that we can conduct data analysis, publish research papers, and ultimately make a more significant impact on the lives of BC patients.

We anticipate that the annual report derived from this registry will provide valuable support to physicians and scientists in comprehending the evolving trends in BC characteristics and treatment modalities in Japan.