Background Trastuzumab emtansine (T-DM1) treatment for human epidermal growth factor receptor-2 (HER2)-positive metastatic breast cancer after taxane with trastuzumab and pertuzumab is standard therapy. However, treatment strategies beyond T-DM1 are still in development with insufficient evidence of their effectiveness. Here, we aimed to evaluate real-world treatment choice and efficacy of treatments after T-DM1 for HER2-positive metastatic breast cancer. Methods In this multi-centre retrospective cohort study involving 17 hospitals, 325 female HER2-positive metastatic breast cancer patients whose post-T-DM1 treatment began between April 15, 2014 and December 31, 2018 were enrolled. The primary end point was the objective response rate (ORR) of post-T-DM1 treatments. Secondary end points included disease control rate (DCR), progression-free survival (PFS), time to treatment failure (TTF), and overall survival (OS). Results The median number of prior treatments of post-T-DM1 treatment was four. The types of post-T-DM1 treatments included (1) chemotherapy in combination with trastuzumab and pertuzumab (n = 102; 31.4%), (2) chemotherapy concomitant with trastuzumab (n = 78; 24.0%), (3), lapatinib with capecitabine (n = 63; 19.4%), and (4) others (n = 82; 25.2%). ORR was 22.8% [95% confidence interval (CI): 18.1–28.0], DCR = 66.6% (95% CI 60.8–72.0), median PFS = 6.1 months (95% CI 5.3–6.7), median TTF = 5.1 months (95% CI 4.4–5.6), and median OS = 23.7 months (95% CI 20.7–27.4). Conclusion The benefits of treatments after T-DM1 are limited. Further investigation of new treatment strategies beyond T-DM1 is awaited for HER2-positive metastatic breast cancer patients.

Breast cancer arising from fibroadenoma (FA) is rare, in which almost all reported cases are human epidermal growth factor receptor 2 (HER2)-negative. This is the first report to describe a case of HER2-positive breast cancer arising from FA that was treated with chemotherapy plus anti-HER2 therapy. In this early case, upfront surgery outcomes guided the selection of appropriate systemic therapy. A 31-year-old woman previously diagnosed with FA experienced tumor growth. Core needle biopsy and imaging studies confirmed a diagnosis of stage IIA HER2-positive invasive ductal carcinoma (IDC) with no evidence of lymph node metastasis (cT2N0M0). Breast-conserving surgery was performed. Pathological diagnosis revealed stage IA IDC with a predominant intraductal component (pT1aN0M0), arising from FA. In conclusion, we encountered an extremely rare case of HER2-positive breast cancer arising from FA in which pathological infiltration was difficult to predict based on preoperative imaging.

Granulomatous mastitis is a rare breast disease that is categorized as a benign tumor with chronic inflammation. Since the cause of the chronic inflammation is usually unknown, it is sometimes called idiopathic granulomatous mastitis (IGM). Although imaging modalities, such as ultrasound, magnetic resonance imaging and mammography can detect tumors, they are sometimes unable to differentiate between benign and malignant tumors. In such cases, biopsy is needed to make a correct diagnosis. We experienced three cases of IGM after breast conserving surgery in breast cancer patients in whom we needed to rule out recurrence of breast cancer. In our cases, tumorectomy was performed in two cases for pathological diagnosis, since neither biopsy nor cytology was able to reveal a conclusive pathological diagnosis. Our management of these three cases might suggest the appropriate management of granulomatous tumors after breast conserving surgery in breast cancer survivors.

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Carney complex (CNC) is a rare multiple tumour syndrome characterized by cutaneous pigmented lesions, myxoma and endocrine tumours, among others, and is inherited as an autosomal dominant trait. Protein kinase cAMP-dependent type I regulatory subunit alpha (PRKAR1A) is known to be the responsible gene. Breast myxomatosis and ductal adenoma, which are regarded as benign, are well-known mammary lesions of CNC and are included in the main diagnostic criteria. In this case, a 59-year-old woman with repeated cardiac myxoma was diagnosed with CNC with PRKAR1A mutation. She also had three multiple breast tumours bilaterally: breast cancer, adenomyoepithelioma and intraductal papilloma. In mammary lesions of CNC, attention should be paid to benign lesions, such as breast myxomatosis or ductal adenomas, and the development of breast cancer or breast tumours with malignant potential. Mammary lesions should be aggressively scrutinized and considered for resection, as required.