Abstract
This annual report of the National Clinical Database-Breast Cancer Registry (NCD-BCR) by the Japanese Breast Cancer Society presents nationwide breast cancer statistics for patients registered in Japan in 2023. Among 107,372 patients with breast cancer at 1317 institutions, 99.3% were females with a median age of 62 years. The distribution of the clinical stages was as follows: stage 0 (15.5%); stage I (42.1%); stage II (31.1%); stage III (7.0%); and stage IV (2.1%). Estrogen receptor, progesterone receptor, and human epidermal growth factor receptor 2 (HER2) positivity was observed in 78.9%, 70.0%, and 13.3% of patients, respectively. Among 102,717 patients without distant metastases, 41.2% underwent breast-conserving surgery, 76.5% underwent sentinel lymph node biopsy, and 6.0% underwent breast reconstruction. The distribution of radiotherapy was as follows: 75.2% received whole-breast irradiation, 15.7% chest-wall irradiation, and 20.7% regional irradiation. Among the 13,061 patients with pT1abN0M0 breast cancer, comprising 10,819 hormone receptor [HR]-positive/HER2-negative, 1479 HER2-positive and 763 HR-negative/HER2-negative individuals, 92.4% of HR-positive/HER2-negative patients received endocrine therapy, 46.9% of HER2-positive patients received chemotherapy and/or anti-HER2 therapy, and 31.2% of HR-negative/HER2-negative patients received chemotherapy. This annual report provides a nationwide overview of contemporary systemic therapy patterns in small breast cancer and highlights size‑dependent and subtype‑specific use of systemic therapy in Japan, reflecting a risk‑adapted treatment strategy.
Keywords: Japanese breast cancer society, Registry, National clinical database, Annual report, Breast neoplasm
Preface
The Japanese Breast Cancer Society initiated the Breast Cancer Registry in 1975. In 2004, it was reorganized into a web-based system in collaboration with the Japan Clinical Research Support Unit, a nonprofit organization, and the Public Health Research Foundation (Tokyo, Japan). In 2012, the registry was integrated into the National Clinical Database–Breast Cancer Registry (NCD-BCR) [1]. The Japanese Breast Cancer Society has developed quality indicators in partnership with the NCD office to offer feedback to breast cancer care providers [1–8]. The details of this system have been described previously. Facilities across Japan have been registering newly diagnosed breast cancer patients in the NCD-BCR. Using these data, institutions can obtain certification for surgical specialty training programs, and surgeons can acquire or renew their professional certifications. The NCD-BCR has also served as the foundation for numerous retrospective observational studies addressing unmet clinical needs [9–24].
Screening mammography has increased the detection of small breast cancers, however, the systemic therapy for pT1abN0 breast cancers remains controversial [25, 26]. At the St. Gallen International Consensus Conference in 2021, many panelists recommended endocrine therapy for hormone receptor (HR)-positive/human epidermal growth factor receptor 2 (HER2)-negative disease, but did not recommend anti-HER2 therapy for HER2-positive disease or chemotherapy for triple-negative disease, particularly in pT1a breast cancer [27]. A previous NCD-BCR study reported that the administration rates of chemotherapy and/or trastuzumab for HER2-positive pT1aN0 and pT1bN0 breast cancer were 20–30% and 50–60% in 2012–2014, respectively [13]. In an observational study led by Japan Clinical Oncology Group, adjuvant endocrine therapy was administered to 83.9% of patients with HR-positive/HER2-negative pT1abN0 breast cancer [28].
This annual report provides an update from the NCD-BCR, summarizing 107,372 breast cancer patients registered in 2023 at 1317 institutions across Japan. Additionally, we present the trends of systemic therapy for small breast cancers.
Demographics and patient characteristics
Of 107,372 patients with breast cancer, 106,655 (99.3%) were women. An overview of the women with breast cancer is summarized in Table 1. The median age at cancer diagnosis was 62 y (interquartile range: 50–73 y). The geographical distribution in Japan was as follows: 4.5% in Hokkaido, 6.4% in Tohoku, 37.1% in Kanto, 15.3% in Chubu, 16.5% in Kinki, 8.5% in Chugoku/Shikoku, and 11.7% in Kyushu. The distribution of clinical stages was as follows: 15.5% in stage 0, 42.1% in stage I, 31.1% in stage II, 7.0% in stage III, and 2.1% in stage IV.
Table 1.
Clinical characteristics of women with breast cancer in 2023
| N | % | |
|---|---|---|
| Geographical distribution | ||
| Hokkaido | 4753 | 4.5 |
| Tohoku | 6823 | 6.4 |
| Kanto | 39,609 | 37.1 |
| Chubu | 16,304 | 15.3 |
| Kinki | 17,646 | 16.5 |
| Chugoku/Shikoku | 9041 | 8.5 |
| Kyushu | 12,466 | 11.7 |
| Others | 13 | 0.0 |
| Age (y), median (IQR) | 62 | 50–73 |
| Menstrual status | ||
| Premenopausal | 30,695 | 28.8 |
| Postmenopausal | 73,141 | 68.6 |
| Unknown | 2819 | 2.6 |
| Family history | ||
| Absence | 80,636 | 75.6 |
| Presence | 21,417 | 20.1 |
| Unknown | 4602 | 4.3 |
| Laterality | ||
| Unilateral | 93,890 | 88.0 |
| Bilateral, synchronous | 7992 | 7.5 |
| Bilateral, metachronous | 4773 | 4.5 |
| Body mass index, kg/m 2 | ||
| −18.5 | 10,823 | 10.1 |
| 18.5–24.9 | 65,695 | 61.6 |
| 25.0–29.9 | 22,163 | 20.8 |
| 30.0–34.9 | 5762 | 5.4 |
| 35.0–39.9 | 1091 | 1.0 |
| 40.0– | 275 | 0.3 |
| Unknown | 846 | 0.8 |
| Clinical T status | ||
| Tis | 16,632 | 15.6 |
| T0 | 432 | 0.4 |
| T1 | 48,139 | 45.1 |
| T2 | 31,544 | 29.6 |
| T3 | 3374 | 3.2 |
| T4 | 5064 | 4.7 |
| Unknown | 1470 | 1.4 |
| Clinical N status | ||
| N0 | 87,341 | 81.9 |
| N1 | 13,182 | 12.4 |
| N2 | 2159 | 2.0 |
| N3 | 2430 | 2.3 |
| Unknown | 1543 | 1.4 |
| Clinical M status | ||
| M0 | 102,717 | 96.3 |
| M1 | 2240 | 2.1 |
| Unknown | 1698 | 1.6 |
| Clinical stage | ||
| 0 | 16,537 | 15.5 |
| I | 44,885 | 42.1 |
| IIA | 24,897 | 23.3 |
| IIB | 8370 | 7.8 |
| IIIA | 2461 | 2.3 |
| IIIB | 3317 | 3.1 |
| IIIC | 1747 | 1.6 |
| IV | 2240 | 2.1 |
| Unknown | 2201 | 2.1 |
Pathology
The pathological findings of 102,717 patients without distant metastases are summarized in Table 2. Noninvasive carcinoma (pTis) was 12.7%, and invasive tumor size 0.1–2.0 cm (pT1) was 51.2%. Of 93,309 patients who underwent axillary surgery, 78.4% had no axillary lymph node metastasis, 16.0% had 1–3 metastases, 3.8% had 4–9 metastases, and 1.8% had ≥ 10 metastases. Estrogen receptor, progesterone receptor, and HER2 were positive in 78.9%, 70.0%, and 13.3% of patients, respectively. Nuclear grade 3 was found in 14.1%, and Ki67 labeling index ≥ 30% was found in 24.7% of patients.
Table 2.
Pathological findings of breast cancer patients without distant metastasis
| N | % | |
|---|---|---|
| Invasive tumor size (cm) † | ||
| 0 | 12,963 | 12.7 |
| 0.1–0.5 | 8148 | 8.0 |
| 0.6–1.0 | 14,655 | 14.3 |
| 1.1–2.0 | 29,566 | 28.9 |
| 2.1–3.0 | 15,409 | 15.1 |
| 3.1–4.0 | 5687 | 5.6 |
| 4.1–5.0 | 2608 | 2.5 |
| 5.1– | 3947 | 3.9 |
| Missing* | 9336 | 9.1 |
| Number of nodal metastasis ‡ | ||
| 0 | 73,172 | 78.4 |
| 1–3 | 14,910 | 16.0 |
| 4–9 | 3569 | 3.8 |
| 10– | 1639 | 1.8 |
| Missing* | 19 | 0.0 |
| Estrogen receptor expression | ||
| Negative | 15,830 | 15.4 |
| 1–9% | 3035 | 3.0 |
| 10%– | 77,997 | 75.9 |
| Missing* | 5855 | 5.7 |
| Progesterone receptor expression | ||
| Negative | 24,654 | 24.0 |
| 1–9% | 7326 | 7.1 |
| 10%– | 64,654 | 62.9 |
| Missing* | 6083 | 5.9 |
| HER2 status | ||
| Negative | 74,607 | 72.6 |
| Positive | 13,632 | 13.3 |
| Missing* | 14,478 | 14.1 |
| Ki67 labeling index | ||
| 0–9% | 23,773 | 23.1 |
| 10–29% | 39,361 | 38.3 |
| 30%– | 25,385 | 24.7 |
| Missing* | 14,198 | 13.8 |
| Nuclear grade † | ||
| 1 | 40,086 | 39.2 |
| 2 | 24,852 | 24.3 |
| 3 | 14,424 | 14.1 |
| Missing* | 22,957 | 22.4 |
HER2 human epidermal growth factor receptor 2
*Including not performed, unknown, and missing values
†Among 102,319 patients who underwent surgery
‡Among 93,309 patients who underwent axillary surgery
Treatment
Surgery
The surgical procedures are summarized in Table 3. Among patients without distant metastases, 41.2%, 52.3%, 2.2%, and 1.9% underwent breast-conserving surgery, mastectomy, nipple-sparing mastectomy, and skin-sparing mastectomy, respectively. Sentinel lymph node biopsy was performed in 76.5% of patients, and axillary lymph node dissection was performed in 20.6% of patients. Breast reconstruction was performed in 6.0% of patients: 3.7% with tissue expander, 0.3% with silicone breast implant, and 1.6% with autologous tissue.
Table 3.
Surgical procedures for breast cancer patients without distant metastasis
| N | % | |
|---|---|---|
| Breast procedure | ||
| None | 163 | 0.2 |
| Breast-conserving surgery | 42,106 | 41.2 |
| Mastectomy | 53,480 | 52.3 |
| Nipple-sparing mastectomy | 2217 | 2.2 |
| Skin-sparing mastectomy | 1900 | 1.9 |
| Others | 415 | 0.4 |
| Unknown | 2038 | 2.0 |
| Axillary procedure | ||
| None | 6825 | 6.7 |
| Sentinel lymph node biopsy | 71,202 | 69.6 |
| Sentinel lymph node biopsy to axillary lymph node dissection | 7054 | 6.9 |
| Axillary lymph node dissection | 14,021 | 13.7 |
| Axillary lymph node sampling | 1032 | 1.0 |
| Others | 57 | 0.1 |
| Unknown | 2128 | 2.1 |
| Breast reconstruction procedure | ||
| None | 94,031 | 94.1 |
| Tissue expander | 3678 | 3.7 |
| Silicone breast implant | 285 | 0.3 |
| Autologous tissue | 1571 | 1.6 |
| Others | 378 | 0.4 |
| Unknown | 2 | 0.0 |
Radiotherapy
An outline of postoperative radiotherapy is summarized in Table 4. The breakdown of the irradiation area is as follows: whole breast ± regional lymph nodes, 81.1%; chest wall ± regional lymph nodes, 15.7%; boost to the tumor bed, 20.7%; and partial breast, 2.2%. Among patients without distant metastasis who underwent breast-conserving surgery, 72.9% received whole-breast irradiation.
Table 4.
Radiotherapy for breast cancer patients without distant metastasis
| N | % | |
|---|---|---|
| Whole breast only | 30,191 | 75.2 |
| Whole breast + regional lymph nodes | 2365 | 5.9 |
| Chest wall only | 619 | 1.5 |
| Chest wall + regional lymph nodes | 5695 | 14.2 |
| Regional lymph nodes only | 248 | 0.6 |
| Others | 1037 | 2.6 |
| Boost to tumor bed | 8298 | 20.7 |
| Partial breast | 885 | 2.2 |
Systemic therapy
The types of perioperative systemic therapies administered to patients without distant metastases are summarized in Table 5. Among 15,311 patients who received neoadjuvant chemotherapy, the pathological complete response (ypT0/isN0) rates were 12.4% for HR-positive/HER2-negative disease, 42.8% for HR-positive/HER2-positive disease, 61.5% for HR-negative/HER2-positive disease, and 39.2% for HR-negative/HER2-negative disease.
Table 5.
Systemic therapy for breast cancer patients without distant metastasis
| Preoperative | Postoperative | |||
|---|---|---|---|---|
| N | % | N | % | |
| Endocrine therapy | ||||
| SERMs | 1257 | 24.4 | 18,031 | 28.0 |
| AIs | 3441 | 66.8 | 40,747 | 63.3 |
| SERMs/AIs +LHRH analogs | 173 | 3.4 | 4667 | 7.2 |
| Others | 282 | 5.5 | 959 | 1.5 |
| Chemotherapy | ||||
| Anthracyclines | 12,682 | 83.8 | 8128 | 40.3 |
| Taxanes | 13,840 | 91.5 | 9121 | 45.2 |
| TC | 320 | 2.1 | 3245 | 16.1 |
| Capecitabine | 38 | 0.3 | 1348 | 6.7 |
| S-1 | 52 | 0.3 | 5242 | 26.0 |
| Carboplatin | 1926 | 12.7 | 121 | 0.6 |
| Others | 516 | 3.4 | 1117 | 5.5 |
| Molecular targeted therapy | ||||
| Trastuzumab | 6118 | 76.1 | 7997 | 54.7 |
| Pertuzumab | 5711 | 71.0 | 5006 | 34.2 |
| Trastuzumab emtansine | 25 | 0.3 | 1800 | 12.3 |
| Bevacizumab | 146 | 1.8 | 34 | 0.2 |
| Olaparib | 4 | 0.0 | 332 | 2.3 |
| Others | 114 | 1.4 | 279 | 1.9 |
AI aromatase inhibitors, LHRH luteinizing hormone releasing hormone, S-1 tegafur/gimeracil/oteracil; SERM selective estrogen receptor modulator, TC docetaxel and cyclophosphamide
Trends in small breast cancer
The number of patients with subcentimeter breast cancer (pT1ab) has increased from 2198 (13.5%) in 2004 to 22,803 (24.0%) in 2023 (Fig. 1). The size-dependent implementation of adjuvant systemic therapy was analyzed in 13,061 patients (10,819 HR-positive/HER2-negative, 1479 HER2-positive and 763 HR-negative/HER2-negative) with pT1abN0M0 breast cancer without preoperative therapy registered in 2023. Among patients with HR-positive/HER2-negative disease, endocrine therapy was administered to 66.9% of those with pT1mi, 83.0% with pT1a, 96.2% with pT1b, and 92.4% of all patients, respectively. Chemotherapy and tegafur/gimeracil/oteracil were infrequently administered (Fig. 2a). Among HER2-positive patients, chemotherapy and/or anti-HER2 therapy was administered to 7.9% of pT1mi, 19.5% of pT1a, 74.9% of pT1b, and 46.9% of all patients. Specifically, anti-HER2 therapy alone was administered to 2.6% of pT1mi, 6.8% of pT1a, 13.4% of pT1b, and 10.1% of all patients (Fig. 2b). In HR-negative/HER2-negative patients, chemotherapy was administered to 1.6% of pT1mi, 9.1% of pT1a, 43.6% of pT1b, and 31.2% of all patients. The predominant regimen was taxane monotherapy (Fig. 2c).
Fig. 1.
Trends in breast cancer incidence between 2004 and 2023 from the Breast Cancer Registry of the Japanese Breast Cancer Society. Size-specific incidence (a) and tumor size distribution (b)
Fig. 2.
Size-dependent implementation of adjuvant systemic therapy for T1abN0M0 breast cancer patients with HR-positive/HER2-negative (a), HER2-positive (b), and HR-negative/HER2-negative (c) in 2023. A, anthracyclines; CT, chemotherapy; ET, endocrine therapy; HER2, human epidermal growth factor receptor 2; HR, hormone receptor; S-1, tegafur/gimeracil/oteracil; T, taxanes
Postscript
In this nationwide registry-based report, we identified clear size-dependent differences in the use of systemic therapy among patients with pT1abN0M0 breast cancer. Across all biological subtypes, treatment intensity increased stepwise from pT1mi to pT1b disease, indicating that tumor size remains a key determinant of therapeutic decision-making in contemporary Japanese clinical practice. Importantly, these observed treatment patterns largely appear to be consistent with current guideline recommendations [25–27]. In particular, the use of chemotherapy and anti-HER2 therapy was markedly lower in pT1mi and pT1a disease, clinical settings in which both international and Japanese guidelines emphasize careful assessment of the balance between potential benefit and overtreatment.
Several limitations of this report should be acknowledged. First, as a registry-based analysis, this report is descriptive in nature and was not designed to evaluate prognosis or causal relationships between treatment and outcomes. Second, treatment decisions were made at the discretion of individual institutions, and heterogeneity in practice patterns across centers may exist. Third, some pathological variables contained a substantial proportion of missing data, which may have affected the detailed characterization of tumor biology. These limitations should be considered when interpreting the present findings.
Detailed information on breast cancer in the NCD-BCR was voluntarily provided by medical staff, including physicians. We greatly appreciate their efforts to analyze data, publish papers, and significantly improve the care of patients with breast cancer. We hope that this annual report will assist physicians and researchers in understanding trends in breast cancer characteristics and treatments in Japan.
Acknowledgements
The authors are grateful all the affiliated institutes participating in the NCD-BCR for their efforts in registering patient data.
Author contributions
Study concept and design: S Sasada. Data assembly: HK and NK. Manuscript writing: S Sasada. Critical revision of the manuscript for important intellectual content: The Committee of Breast Cancer Registry and Data Science of JBCS (HK, T Iwamoto, MK, T Konishi, S Saji, NS, KT, MN, MM, MY, T Kinoshita, YS, NN, T Ishida, NT) and NK. Final approval of the manuscript: All authors.
Funding
Open Access funding provided by Hiroshima University. This work was supported by the Registration Committee of the Breast Cancer Registry and Data Science.
Data availability
The NCD-BCR is not publicly accessible owing to the sensitive nature of clinical information. Access was granted to a designated statistician through an application process approved by relevant academic societies. Therefore, we were unable to share the original data from this study.
Declarations
Conflict of interest
Grants or contracts from any entity—S Sasada: Chugai, Daiichi-Sankyo, Eli Lilly, Gilead Sciences, and Nipro; HK: Amgen, National Clinical Database, and Pfizer. MK: Advalife Science, Chugai/Roche, Eli Lilly, Fujiwara Memorial Foundation, JBCRG, and Merck; S Saji: AstraZeneca, Chugai, Daiichi-Sankyo, Eisai, Eli Lilly, Gilead Sciences, MSD, Sanofi, Taiho, and Takeda; NN: Boehringer Ingelheim, Chugai, Daiichi-Sankyo, Eisai, and Novartis; NT: Chugai, Daiichi-Sankyo, Eisai, Eli Lilly, Kyowa Kirin, and Taiho. Consulting fees—HK: EPS corporation; MY: Roche. Payment or honoraria for lectures—S Sasada: Chugai, Daiichi-Sankyo, Eisai, Eli Lilly, Kyowa Kirin; HK: Novartis; MK: AstraZeneca, Chugai, Daiichi-Sankyo, Devicor Medical, Eisai, Guardant Health AMEA, and Pfizer; S Saji: AstraZeneca, Chugai, Daiichi-Sankyo, Eisai, Eli Lilly, Exact Sciences, Gilead Sciences, Kyowa Kirin, MSD, Nippon Kayaku, Novartis, Ono, Pfizer, Taiho, and Takeda; MN: AstraZeneca, Chugai, Daiichi-Sankyo, Eisai, Eli Lilly, Exact Sciences, Kyowa Kirin, MSD, Pfizer, and Taiho; MM: AstraZeneca, Chugai, Daiichi-Sankyo, Eli Lilly, Exact Sciences, Gilead Sciences, MSD, and Pfizer; MY: Agilent Technologies, Chugai, Daiichi-Sankyo, MSD, Ono, and Roche. YS: AstraZeneca, Chugai, Daiichi-Sankyo, Eisai, Eli Lily, Kyowa Kirin, MSD, Nippon Kayaku, Pfizer, and Sysmex; NN: AstraZeneca, Chugai, Daiichi-Sankyo, Eli Lilly, MSD, and Pfizer; NT: AstraZeneca, Boehringer Ingelheim, Chugai, Daiichi-Sankyo, Eisai, Eli Lilly, Kyowa Kirin, MSD, Pfizer, and Takeda. Participation on a Data Safety Monitoring Board or Advisory Board—T Konishi: Health Insurance Claims Review and Reimbursement Services. S Saji: AstraZeneca, Chugai/Roche, Daiichi-Sankyo, Eli Lilly, Kyowa Kirin, MSD, and Pfizer; MY: Daiichi-Sankyo. Leadership or fiduciary role—S Saji: JBCRG, and JBCS. Stock or stock options— S Sasada: Daiichi-Sankyo.Other financial or non-financial interests—HK: affiliation to the social collaboration department at the University of Tokyo supported by the National Clinical Database, Intuitive Surgical Sarl, Johnson and Johnson, and Nipro; NK: employed as a specially appointed academic staff member with funding provided by National Clinical Database. NT: director of the Japanese Breast Cancer Society, and chairperson of the Registration Database Committee of the Japanese Breast Cancer Society.
Ethical approval
This article does not contain any animal studies conducted by any of the authors. All procedures involving human participants performed in this study were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards.
Informed consent
Formal consent was not required for this study.
Footnotes
Publisher’s Note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Data Availability Statement
The NCD-BCR is not publicly accessible owing to the sensitive nature of clinical information. Access was granted to a designated statistician through an application process approved by relevant academic societies. Therefore, we were unable to share the original data from this study.