Aim:With the aggregation of real-world data in healthcare, opportunities for outcomes research are growing. In this study, we summarize published literature examining comparative effectiveness research (CER), treatment patterns, quality of life (QoL) and costs in HER2-negative and triple-negative (TN) metastatic breast cancer (mBC). Methods: PubMed (2010-January 2016) and four conferences (2013-January 2016) were searched using MeSH/keywords, including mBC, QoL, morbidity and therapeutics. Studies relating to CER, treatment patterns, QoL, costs or treatment appropriateness in US patients with HER2-negative/TN mBC were included in the review. Results: Of 1782 identified records, 33 studies met full inclusion criteria: seven related to CER, 18 to treatment patterns, one to treatment appropriateness/navigation, two to QoL and five to costs. Studies varied in objectives, designs and outcomes. Study designs included retrospective chart reviews (52%), retrospective secondary database analyses (27%), economic models (12%), physician surveys (6%) and patient surveys (3%). 25 studies reported results on HER2-negative mBC, six on TN mBC and two on both subtypes. The most common end points examined were treatment patterns, overall survival and progression-free survival. Conclusion: Outcomes research in HER2-negative mBC in the USA was limited, specifically among TN patients, indicating an opportunity for further research in this high unmet need population. Endpoints and treatment options varied, thus, it is difficult to draw summary conclusions about these studies. Outcomes research examining real-world data in mBC has increased in recent years, and may continue to grow with the implementation of new policy programs. Breast cancer is the most common cancer type among women in the USA. 29% of incident cancer cases are attributable to breast cancer alone [1]. About 66% of women with breast cancer have HER2-negative and 10-17% have HER2-negative, estrogen receptor-negative (ER-negative) and progesterone receptor-negative (PR-negative) cancer, referred to as triple-negative breast cancer (TNBC) [2,3]. In 2016, an estimated 246,660 women were newly diagnosed with breast cancer, of which approximately 6% had metastatic or stage IV disease at the time of diagnosis [1,4,5]. About 30% of women initially diagnosed with early-stage breast cancer develop recurrent advanced or metastatic disease [6,7]. The 5-year survival rate with stage IV breast cancer is only 26.3% [4,5].Tumor markers in breast cancer impact prognosis, treatment and survival [8]. Prognosis has improved significantly for patients with metastatic HER2-positive breast cancer with emergence of trastuzumab and other anti-HER2 agents but has lagged for patients with advanced HER2-negative breast cancer since the emergence of effective new targeted therapies such as everolimus is only beginning [9]. Moreover, an important minority of these patients, those with triple-negative (TN) disease, has a relatively poor prognosis given the lack of targeted therapies, leaving cytoto...