Clinical application of targeted tumour sequencing tests for detecting ERBB2 amplification and optimizing anti-HER2 therapy in gastric cancer.

BACKGROUND: Evaluation of human epidermal growth factor receptor 2 (HER2) overexpression caused by erb-b2 receptor tyrosine kinase 2 (ERBB2) amplification (AMP) by immunohistochemistry (IHC) and fluorescence in situ hybridization (FISH) is essential for treating unresectable metastatic gastric cancer (GC). A targeted tumour sequencing test enables comprehensive assessment of alterations in cancer-related genes, including ERBB2. This study aimed to evaluate the concordance between the targeted tumour sequencing test and IHC/FISH for detecting HER2-positive GC and to clarify the significance of ERBB2 AMP and concomitant genetic alterations in HER2 downstream pathways (DPs) in anti-HER2 therapy for unresectable metastatic GC patients. METHODS: ERBB2 copy number alteration (CNA) was examined via a targeted tumour sequencing test in 152 formalin-fixed paraffin-embedded (FFPE) GC tissues. ERBB2 CNA was compared to HER2 status evaluated by IHC/FISH in FFPE block sections, which were identical to those subjected to the targeted tumour sequencing test. Treatment outcomes of anti-HER2 therapy in 11 patients with unresectable metastatic GC was evaluated. RESULTS: ERBB2 AMP (≥ 2.5-fold change) was detected by the targeted tumour sequencing test in 15 patients (9.9%), and HER2 positivity (IHC 3 + or IHC 2+/FISH positive) was detected in 21 patients (13.8%). The overall percent agreement, positive percent agreement, negative percent agreement and Cohen's kappa between ERBB2 CNA and HER2 status were 94.7%, 66.7%, 99.2% and 0.75, respectively. Progression-free survival for trastuzumab therapy in patients with ERBB2 AMP was significantly longer than that in patients with no ERBB2 AMP detected by the targeted tumour sequencing test (median 14 months vs. 4 months, P = 0.007). Treatment response to trastuzumab therapy was reduced in patients with ERBB2 AMP and concomitant CNAs of genes in HER2 DPs. One patient with ERBB2 AMP and concomitant CNAs of genes in HER2 DPs achieved a durable response to trastuzumab deruxtecan as fourth-line therapy. CONCLUSIONS: A targeted tumour sequencing test is a reliable modality for identifying HER2-positive GC. ERBB2 AMP and concomitant genetic alterations detected through the targeted tumour sequencing test are potential indicators of treatment response to trastuzumab therapy. The targeted tumour sequencing test has emerged as a plausible candidate for companion diagnostics to determine indications for anti-HER2 therapy in the era of precision medicine for GC.

Landscape of homologous recombination deficiency in gastric cancer and clinical implications for first-line chemotherapy.

BACKGROUND: Homologous recombination deficiency (HRD) is one of the crucial hallmarks of cancer. It is associated with a favorable response to platinum-based chemotherapy. We explored the distinctive clinicopathological features of gastric cancer (GC) with HRD and the clinical significance of HRD in platinum-based first-line chemotherapy for unresectable metastatic GC. METHODS: We enrolled 160 patients with GC in this study. Their tumor samples were subjected to genomic profiling utilizing targeted tumor sequencing. HRD was defined as the presence of alterations in any of 16 HR genes (BARD1, BLM, BRCA1, BRCA2, BRIP1, MRE11A, NBN, PALB2, PARP1, POLD1, RAD50, RAD51, RAD51C, RAD51D, WRN, and XRCC2). The clinicopathological features and treatment outcomes of first-line chemotherapy for unresectable metastatic GC were compared between HRD and non-HRD groups. RESULTS: Forty-seven patients (29.4%) were classified into the HRD group. This group had a significantly lower proportion of macroscopic type 3 or 4 tumors and higher TMB than the non-HRD group. Among patients who underwent platinum-based first-line chemotherapy, the HRD group had a greater response rate and longer progression-free survival after treatment (median 8.0 months vs. 3.0 months, P = 0.010), with an adjusted hazard ratio of 0.337 (95% confidence interval 0.151-0.753). HRD status was not associated with treatment outcomes in patients who did not undergo platinum-based chemotherapy. CONCLUSIONS: Low proportion of macroscopic type 3 or 4 tumors and a high TMB are distinctive features of GC with HRD. HRD status is a potential predictive marker in platinum-based first-line chemotherapy for unresectable metastatic GC.

[Cancer of the Ascending Colon and Left Breast in an Older Adult Complicated by Thoracic Aortic Aneurysm].

An 87-year-old woman with a gradually enlarging mass in her left breast, diagnosed as having left-sided breast cancer with skin invasion by a local practitioner, was referred to our hospital. Computed tomography revealed ascending colon cancer with abdominal wall invasion and a thoracic aortic aneurysm(Stanford type B), in addition to breast cancer with skin invasion. A thoracic endovascular aortic repair and bypass surgery between the subclavian arteries were both performed for the thoracic aortic aneurysm. After 6 days, a right hemicolectomy and D2 lymphadenectomy were performed for the ascending colon cancer. A postoperative pathological diagnosis of pT3N0M0, pStage Ⅱa, was made. A total left mastectomy with a full-thickness skin graft for left breast cancer was performed after 2 months following the ascending colon cancer surgery. The postoperative pathological diagnosis was pT3N0M0, pStage ⅡB. No evidence of local recurrence or distant metastasis of the ascending colon cancer has been observed at 20 months postoperatively, or of the breast cancer after 18 months following surgery.

[A Case of Esophageal Carcinoma with Tracheal Invasion after Preoperative Treatment with Docetaxel, Cisplatin, and 5-Fluorouracil in Which Definitive Chemoradiotherapy and Salvage Esophagectomy Prolonged Survival].

A 57-year-old man was diagnosed as having resectable advanced esophageal carcinoma adjacent to the trachea(Ut, cT3N0M0)and received preoperative docetaxel, cisplatin, and 5-fluorouracil therapy. Due to tracheal tumor invasion and upstaging to cT4bN0M0 after 1 course of chemotherapy, the treatment was converted to definitive chemoradiotherapy (CRT). A remarkable response with no evidence of tracheal invasion was observed on computed tomography following definitive CRT. He underwent successful curative resection with salvage esophagectomy, and the resected tumor was staged as pT1bN0M0. No adjuvant therapy was administered, and the patient was alive with no evidence of disease at the 5-year postoperative follow-up. The response to preoperative treatment should be meticulously assessed and appropriate treatment modalities used to avoid overlooking the potential for cure, even if the response to preoperative treatment with docetaxel, cisplatin, and 5-fluorouracil is poor.

Plasma Sphingosine-1-Phosphate Levels Are Associated with Progression of Estrogen Receptor-Positive Breast Cancer.

Although numerous experiments revealed an essential role of a lipid mediator, sphingosine-1-phosphate (S1P), in breast cancer (BC) progression, the clinical significance of S1P remains unclear due to the difficulty of measuring lipids in patients. The aim of this study was to determine the plasma concentration of S1P in estrogen receptor (ER)-positive BC patients, as well as to investigate its clinical significance. We further explored the possibility of a treatment strategy targeting S1P in ER-positive BC patients by examining the effect of FTY720, a functional antagonist of S1P receptors, on hormone therapy-resistant cells. Plasma S1P levels were significantly higher in patients negative for progesterone receptor (PgR) expression than in those positive for expression (p = 0.003). Plasma S1P levels were also significantly higher in patients with larger tumor size (p = 0.012), lymph node metastasis (p = 0.014), and advanced cancer stage (p = 0.003), suggesting that higher levels of plasma S1P are associated with cancer progression. FTY720 suppressed the viability of not only wildtype MCF-7 cells, but also hormone therapy-resistant MCF-7 cells. Targeting S1P signaling in ER-positive BC appears to be a possible new treatment strategy, even for hormone therapy-resistant patients.

[A Case of HER2-Positive Recurrent Breast Cancer and Liver Metastases of GIST Treated with Combined Anti-HER2 Therapy and Imatinib].

A 70-year-old female with liver metastases from gastrointestinal stromal tumor(GIST)that were found 3 months after partial gastrectomy for the primary GIST underwent Auchincloss operation for left breast cancer with ipsilateral axillary lymph node metastases. The diagnosis was microinvasive ductal cancer that was pT1miN1M0, pStage ⅡA, hormone receptor negative, and HER2 positive. Given the impact of this cancer on the prognosis of liver metastases of GIST, imatinib therapy, but not adjuvant chemotherapy, was started promptly for breast cancer after surgery. Four months after the surgery, left subclavian lymph node recurrence of breast cancer was found. Since the liver metastases of GIST had been stable, imatinib was discontinued, and paclitaxel and anti-HER2 therapy were administered. After confirming tolerability, imatinib was carefully added in combination. Because the lymph nodes shrank and liver metastases of GIST were stable, both anti-HER2 therapy and imatinib were continued. There are few reports of combined chemotherapy for synchronous double cancer, and we report our experience in which careful treatment was required.

[A Case of Invasive Lobular Carcinoma of Accessory Mammary Gland That Was Difficult for Evaluate for Lesion Spread].

A 48-year-old female discovered a mass in her left axilla. A thorough examination resulted in a diagnosis of left invasive lobular carcinoma(ILC)of the accessory mammary gland with wide ductal spread. Considering the wide ductal spread, massive resection of the left axilla mass, left lymph node dissection, and a latissimus dorsi musculocutaneous flap procedure were performed. However, histological analysis revealed ILC measuring 80×50 mm with lymph node metastases(5/23)and extensive cancer spread, resulting in a positive surgical margin. It is important to recognize the characteristics of ILC, axillary accessory breast cancer, and the axilla in a treatment strategy.

[A Case of High-Frequency Microsatellite Instability in Colorectal Cancer with MSH2 Mutation Detected Using Gene Panel Testing with a Next-Generation Sequencer].

Here, we report about a woman in her 30s who had peritoneal dissemination and multiple colon cancer with high-frequency microsatellite instability(MSI-H). Her father, paternal grandfather, and maternal grandmother had a history of colorectal cancer treatment. Thus, Lynch syndrome was suspected. We performed R0 resection for peritoneal dissemination and subsequent peritoneal dissemination. A 435-gene panel testing using a next-generation sequencer identified MSH2 and other mutations in the tumor. Hence, we speculated that she could have a germline mutation of MSH2, which causes Lynch syndrome. In the future, if she wishes to receive genetic counseling and undergo germline testing for variants to confirm the diagnosis of Lynch syndrome, we will perform them after receiving informed consent.

Early-stage T1b adenocarcinoma arising in the remnant cystic duct after laparoscopic cholecystectomy: a case report and literature review.

BACKGROUND: The cystic duct has been included in the staging classification scheme for gallbladder cancer since the 2010 publication of the AJCC Cancer Staging Manual (7th edition). To our knowledge, only seven other cases of adenocarcinoma arising in the remnant cystic duct following cholecystectomy have been reported in the English-language literature, and none has been reported as primary early-stage T1b remnant cystic duct cancer (CDC). We report, herein, a case of primary adenocarcinoma arising in the remnant cystic duct in a patient with history of laparoscopic cholecystectomy for gallstone disease. CASE PRESENTATION: An 81-year-old female presented with abdominal pain. Her medical history included a laparoscopic cholecystectomy for cholecystolithiasis two years prior. Jaundice was observed; imaging studies suggested that this was caused by choledocholithiasis. Blood chemistry findings showed severe liver dysfunction. Endoscopic retrograde cholangiography revealed haemobilia from the common bile duct with no evidence of choledocholithiasis. A bile sample showed Papanicolaou class IV cytology. As the extent of tumour spread was undetermined by abdominal ultrasonography and endoscopic ultrasonography, peroral cholangioscopy (POCS) was performed, which revealed tiny papillary lesions within the confluence of cystic duct, and fine granular lesions in the centre of bile ducts, signifying early-stage remnant CDC. Extrahepatic bile duct resection with regional lymphadenectomy was done. Histopathological findings revealed a 42-mm tubular adenocarcinoma originating from the remnant cystic duct with the considerable shallow spread across the extrahepatic bile ducts. It invaded the fibromuscular layer, with no lymphovascular or perineural invasion, no lymph node metastasis (13 nodes examined), and uninvolved surgical resection margin (R0 resection), and was staged as pT1bN0M0, Stage I. CONCLUSIONS: Primary early-stage T1b remnant CDC is an uncommon condition for which early diagnosis is challenging; if intraoperatively recognized, it can complicate surgery. Our experience of this case and an overview of the English literature suggest that POCS is an efficient tool to diagnosis this tumour and assess its spread along the extrahepatic bile ducts.

[A Case of Metachronal Phyllodes Tumors That Presented Bilaterally in the Breast].

A 33-year-old woman underwent resection of a right breast mass, which was diagnosed as a fibroadenoma 15 years ago. Ten years later, a right breast mass appeared again, and it was diagnosed as a fibroadenoma based on core needle biopsy. After observation for a while, the mass increased in size, and she underwent resection of the tumor, which was diagnosed as a borderline-malignant phyllodes tumor. A mass appeared again in the right breast and rapidly expanded. A malignant phyllodes tumor was suspected, and right mastectomy was performed. The pathological diagnosis revealed a benign phyllodes tumor. Four years ago, a left breast mass was also detected. Because the mass was suspected to be a fibroadenoma, it has been observed for a few years. The mass has increased in size since 1 year ago, and another mass emerged 2 months ago. Core needle biopsy of the 2 masses revealed that both were phyllodes tumors. She underwent left mastectomy, and the pathological examination revealed that both masses were benign phyllodes tumors. We report this rare case of metachronal phyllodes tumors that presented bilaterally.

[A Case of Breast Cancer with Metastatic Nodules in Additionally Resected Specimens].

A 68-year-old woman who had leftbreastcancer (cT2N0M0, cStage ⅡA)underwentbreast -conserving therapy and sentinel lymph node biopsy. Pathological diagnosis of the resected specimen revealed a 60mm cancer lesion including a 50 mm invasive ductal carcinoma with surrounding ductal carcinoma in situ, although the pre-operative MRI suggested a 30mm invasive cancer. The surgical margin was positive with the exposure of ductal carcinoma in situ. Additional resection was performed with a resection margin of 20mm from the head-side stump of the previous surgery. Pathological diagnosis of the additionally resected specimen revealed a 6mm invasive carcinoma with its exposure on the surface of the specimen around the new surgical stump distant from the initial surgical margin, where no remnant cancer was noted. She underwent left mastectomy. Pathological diagnosis further revealed 7mm and 2mm invasive carcinomas in the remnant breast. The preoperative imaging was reviewed retrospectively, and it was found that identifying the nodules in the remnant breast was quite difficult based on the images, including MRI. We report a case of breast cancer with metastatic nodules in additionally resected specimens.

[Clinical Experience of a Primary Accessory Breast Cancer Patient].

A 59-year-old woman attended a previous hospital complaining of a nodule of the right axilla. Although ultrasonography had shown no evidenceof malignancy, a growth of thenodulewas found on follow-up. Excisional biopsy revealed a primary accessory breast cancer. Because the resected margins were involved, she was referred to our hospital for additional treatment. Based on imaging, both bilateral mammary glands and axillary lymph nodes were reported normal, and distant metastasis was not observed. We performed additional resection of the right axillary tissue around the biopsy site and the right axillary lymph nodedisse ction. Histo-pathological examination revealed the residual invasive ductal carcinoma in the resected specimen. Both the new surgical margins and the lymph nodes were free of disease. Accessory breast cancer is relatively rare, with the incidence being less than 1% of all breast cancers. It is most frequent in the axillary region. Local extensive resection with sufficient surgical margin and axillary lymph node dissection are generally required. This case report presents our clinical experience of accessory breast cancer with some discussion of the literature.

High levels of sphingolipids in human breast cancer.

BACKGROUND: Sphingolipids, including sphingosine-1-phosphate (S1P) and ceramide, have emerged as key regulatory molecules that control various aspects of cell growth and proliferation in cancer. Although important roles of sphingolipids in breast cancer progression have been reported in experimental models, their roles in human patients have yet to be determined. The aims of this study were to determine the levels of sphingolipids including S1P, ceramides, and other sphingolipids, in breast cancer and normal breast tissue and to compare the difference in levels of each sphingolipid between the two tissues. MATERIALS AND METHODS: Tumor and noncancerous breast tissue were obtained from 12 patients with breast cancer. Sphingolipids including S1P, ceramides, and their metabolites of sphingosine, sphingomyelin, and monohexosylceramide were measured by liquid chromatography-electrospray ionization-tandem mass spectrometry. RESULTS: The levels of S1P, ceramides, and other sphingolipids in the tumor were significantly higher than those in normal breast tissue. There was a relatively strong correlation in the levels of S1P between the tumor and those of normal breast tissue from the same person. On the other hand, there was no correlation in the levels of most of the ceramide species between the tumor and those of normal breast tissue from the same person. CONCLUSIONS: To our knowledge, this is the first study to reveal that levels of sphingolipids in cancer tissue are generally higher than those of normal breast tissue in patients with breast cancer. The correlation of S1P levels in these tissues implicates the role of S1P in interaction between cancer and the tumor microenvironment.

Breast cancer sphingosine-1-phosphate is associated with phospho-sphingosine kinase 1 and lymphatic metastasis.

BACKGROUND: Sphingosine-1-phosphate (S1P), a pleiotropic bioactive lipid mediator, has been implicated as a key regulatory molecule in cancer through its ability to promote cell proliferation, migration, angiogenesis, and lymphangiogenesis. Previous studies suggested that S1P produced by sphingosine kinase 1 (SphK1) in breast cancer plays important roles in progression of disease and metastasis. However, the associations between S1P and clinical parameters in human breast cancer have not been well investigated to date. MATERIALS AND METHODS: We determined levels of S1P and other sphingolipids in breast cancer tissue by electrospray ionization-tandem mass spectrometry. Associations between S1P levels and clinicopathologic features of the tumors were analyzed. Expression of phospho-SphK1 (pSphK1) in breast cancer tissues was determined by immunohistochemical scoring. RESULTS: Levels of S1P in breast cancer tissues were significantly higher in patients with high white blood cell count in the blood than those patients without. S1P levels were lower in patients with human epidermal growth factor receptor 2 overexpression and/or amplification than those patients without. Furthermore, cancer tissues with high pSphK1 expression showed significantly higher levels of S1P than cancer tissues without. Finally, patients with lymph node metastasis showed significantly higher levels of S1P in tumor tissues than the patients with negative nodes. CONCLUSIONS: To our knowledge, this is the first study to demonstrate that high expression of pSphK1 is associated with higher levels of S1P, which in turn is associated with lymphatic metastasis in breast cancer.

DNA damage response and sphingolipid signaling in liver diseases.

Patients with unresectable hepatocellular carcinoma (HCC) cannot generally be cured by systemic chemotherapy or radiotherapy due to their poor response to conventional therapeutic agents. The development of novel and efficient targeted therapies to increase their treatment options depends on the elucidation of the molecular mechanisms that underlie the pathogenesis of HCC. The DNA damage response (DDR) is a network of cell-signaling events that are triggered by DNA damage. Its dysregulation is thought to be one of the key mechanisms underlying the generation of HCC. Sphingosine-1-phosphate (S1P), a lipid mediator, has emerged as an important signaling molecule that has been found to be involved in many cellular functions. In the liver, the alteration of S1P signaling potentially affects the DDR pathways. In this review, we explore the role of the DDR in hepatocarcinogenesis of various etiologies, including hepatitis B and C infection and non-alcoholic steatohepatitis. Furthermore, we discuss the metabolism and functions of S1P that may affect the hepatic DDR. The elucidation of the pathogenic role of S1P may create new avenues of research into therapeutic strategies for patients with HCC.

[Study of Breast Cancer Patients Diagnosed Preoperatively with Ductal Carcinoma In Situ].

Although ductal carcinoma in situ(DCIS)is generally cured by surgical resection, it has been suggested that resection is over-treatment for some patients with DCIS. The aim of this study was to reconsider operative indications for patients with DCIS by examining clinicopathological features of 23 patients who underwent surgical resection for DCIS in our institute over a single year. Postoperative histological examination revealed that there were Luminal and HER2-positive subtypes, but no triple negative cancers. We found coincidental invasive ductal carcinoma(IDC)in 5 patients, and in all 5 the tumor size exceeded 60 mm. There was no coincidence of IDC in patients with a Ki-67 index ≤5%. Positive surgical margins were observed in 7 patients, all of which were histologically diagnosed as DCIS. Only 1 of the 7 patients underwent additional surgical resection; the 6 remaining patients, including 2 patients who received no treatment, did not undergo additional resection. All patients including those with positive surgical margins have had a 5-year relapse-free survival. Our findings imply that the subgroup of DCIS patients without IDC could be followed up without surgery.

[A Case of Minimally Invasive Apocrine Carcinoma Derived from Ductal Adenoma].

A 63-year-old woman was found to have a mass in her right breast and visited our hospital to undergo a detailed examination. A histopathological examination by using ultrasound-guided core needle biopsy revealed ductal carcinoma in situ. A partial mastectomy with sentinel lymph node biopsy was performed for the cancer of the right breast. The postoperative histopathological examination indicated apocrine carcinoma with a predominantly intraductal component without lymph node metastasis. The discrimination between ductal adenoma and apocrine carcinoma sometimes becomes a problem in making decisions about treatment. We need to take care when making a diagnosis.

[Locally Advanced Breast Cancer Treated with Halsted's Operation Because of Drug-Induced Lung Injury Caused by Neoadjuvant Chemotherapy--A Case Report].

A 64-year-old woman discovered a mass in her left breast and visited our hospital. A thorough examination resulted in a diagnosis of left, locally advanced breast cancer (cT4bN3, M0, cStage Ⅲc) with muscle invasion and Level Ⅲ lymph node metastases. Because of drug-induced lung disease following 4 courses of adriamycin and cyclophosphamide, the chemotherapy had to be stopped. Halsted's operation and postoperative radiotherapy (50 Gy) were performed. The patient was alive with no evidence of recurrence 9 months after surgery. Although multidisciplinary therapy is recommended in locally advanced breast cancer, chemotherapy sometimes cannot be performed due to factors such as age and physical status. Halsted's operation could be considered as a treatment of choice in patients with locally advanced breast cancer. It is important to choose the treatment strategy based on the condition of the patient.

Prognostic Significance of NQO1 Expression in Non-neoplastic Esophageal Squamous Epithelium for Patients With Esophageal Cancer.

BACKGROUND/AIM: NAD(P)H dehydrogenase [quinone] 1 (NQO1), an antioxidant enzyme, confers resistance to anticancer agents. NQO1 C609T is a single-nucleotide polymorphism associated with reduced protein expression in the non-neoplastic esophageal squamous epithelium (ESE). This study aimed to investigate immunohistochemical NQO1 expression in non-neoplastic ESE and to elucidate its prognostic significance in patients with esophageal squamous cell carcinoma (ESCC) undergoing neoadjuvant therapy followed by esophagectomy. MATERIALS AND METHODS: NQO1 expression in non-neoplastic ESE was determined in surgical specimens from 83 patients with ESCC using immunohistochemistry. The association between NQO1 expression and clinicopathological factors, and the prognostic significance of NQO1 expression for relapse-free survival (RFS) were statistically evaluated. RESULTS: Patients with complete loss or weak NQO1 expression and patients with moderate or strong NQO1 expression were classified into the NQO1-negative (n=29) and NQO1-positive (n=54) groups, respectively. The downstaging of T classification status after neoadjuvant therapy was significantly more frequent in the NQO1-negative group than in the NQO1-positive group (59% vs. 33%; p=0.036). The NQO1-negative group had significantly more favorable RFS than the NQO1-positive group (p=0.035). Multivariate survival analysis demonstrated that NQO1 negative expression had a favorable prognostic impact on RFS (HR=0.332; 95%CI=0.136-0.812; p=0.016). CONCLUSION: Immunohistochemical evaluation of NQO1 expression in non-neoplastic ESE has clinical utility for predicting patient prognosis after neoadjuvant therapy followed by esophagectomy and might be helpful for selecting candidates for adjuvant therapy to treat ESCC.

Increasing survivors of anthracycline-related cardiomyopathy with breast cancer in trastuzumab era: thirty-one-year trends in a Japanese Community.

BACKGROUND: Trastuzumab has improved breast cancer (BC) prognosis and reduced anthracycline use. However, the characteristic changes of anthracycline-related cardiomyopathy (ARCM) in patients with BC remain unclear. We aimed to update our understanding of ARCM in the trastuzumab era. METHODS: This retrospective observational cohort study included 2959 patients with BC treated with anthracyclines at three regional cancer centers in Niigata City between 1990 and 2020. Seventy-five patients (2.5%) developed ARCM and were categorized into two groups: pre- 2007 (early phase) and post-2007 (late phase), corresponding to before and during the trastuzumab era in Japan. RESULTS: ARCM incidence peaked at 6% in the 1990s, then decreased and stabilized at 2% until the 2010s. Survivors of anthracycline-treated BC increased more rapidly in the late phase, with four times as many patients with ARCM compared to the end of the early phase (26 and six, respectively). Although the rate of change in accumulation from the early phase to the late phase was slight in the anthracycline-treated BC group, it was more pronounced in the ARCM group (P < 0.001). Mean anthracycline use in the late phase was significantly lower than in the early phase (307 vs. 525 mg/m2, P < 0.001). Five-year survival rates in the late phase tended to be higher than early phase (45% and 28%, respectively. P = 0.058). Human epidermal growth factor receptor type 2 (HER2) positivity with trastuzumab therapy in the late phase was an independent predictor for mortality within 10 years (hazard ratio = 0.24, 95% confidence interval: 0.10-0.56; P = 0.001). CONCLUSIONS: HER2-positive patients with ARCM receiving trastuzumab therapy had a better prognosis than HER2-positive and HER2-negative patients with ARCM not receiving trastuzumab therapy, and this trend has been increasing in the trastuzumab era. These findings highlight the importance of HER2-targeted treatments in improving prognosis for BC patients with ARCM.