BackgroundBreast cancer is the most common cancer in women worldwide. Cancer-secreted exosomes have recently been recognized as important mediators of intercellular communication. The aim of this study was to determine the role of exosomal long noncoding RNA metastasis-associated lung adenocarcinoma transcript 1 (MALAT1) in breast cancer progression.Materials and methodsBreast cancer specimens were obtained with informed consent from patients. Quantitative real-time polymerase chain reaction (qRT-PCR) was used to detect MALAT1 expression, and cellular proliferation was measured using cell counting kit-8 (CCK-8) assay.ResultsMALAT1 was highly expressed in breast cancer tissues and associated with disease progression. Breast cancer exosomes promoted cell proliferation and exosome-mediated MALAT1 to induce cell proliferation.ConclusionThese findings indicated that exosomal MALAT1 could regulate cancer progression and represent a novel strategy for overcoming breast cancer.

<b><i>Introduction:</i></b> Mucinous breast carcinoma is a rare histologic subtype of primary breast cancers accounting for 1–6%. It is a rare histological variant in young patients and usually presents without lymph node involvement, and its pathological response to neoadjuvant chemotherapy is rarely reported. <b><i>Case Presentation:</i></b> Pure mucinous breast carcinoma in a 25-year-old female was treated with neoadjuvant chemotherapy every 3 weeks for 8 cycles. After the fifth cycle, the mass size showed no change. We performed modified radical mastectomy in the left breast and axillary lymph node clearance. However, the pathological report showed a complete elimination of both the breast tumor and axillary lymph nodes, which were filled with mucus but did not contain malignant cells <b><i>Discussion:</i></b> Chemotherapy was profoundly effective against the tumor cells, but ineffective against large amounts of extracellular mucus. Even though the cancer cells were sensitive to chemotherapy, the volume of mucinous cancer couldnot be reduced. <b><i>Conclusion:</i></b> In summary, the evaluation criteria of tumor response to chemotherapy based on maximum diameter only should be considered insufficient for mucinous carcinoma.