Benefits of chemotherapy vary in patients with metastatic breast cancer (MBC). This article describes the impact of tumor subtype and the line of therapy on the duration of chemotherapy. Clinicopathologic characteristics were extracted from the medical records of 199 consecutive patients with MBC at Dana-Farber Cancer Institute and analyzed according to subtype. Tumor subtypes were classified as hormone receptor (HR)-positive, triple-negative (TNBC), or HER2-amplified breast cancer. Duration of chemotherapy of each line was defined as the start of a chemotherapy regimen to the start of the next line of therapy as a result of progression or toxicity. There were 96, 44, and 59 patients with HR(+), TNBC, and HER2-amplified breast cancer, respectively. Median age at MBC diagnosis was 53 years. Median overall survivals were 32 and 54 months for HER2-amplified disease, 36 months for HR(+) breast cancer, and 17 months for TNBC (P<.0001). Patients with HER2-amplified disease received the most lines (median, 4; P=.032) and the longest duration of chemotherapy for every line. The median duration of chemotherapy in HER2-amplified patients remained at more than 4 months even out to sixth-line therapy. Patients with TNBC tended to receive the shortest duration of chemotherapy for every line of therapy. Tumor subtypes influence the number of lines, duration of chemotherapy, and survival. Among patients with HR(+) and HER2-amplified disease who undergo chemotherapy beyond the third line, substantial rates of prolonged therapies suggest clinical benefit. The role of advanced (greater than third) chemotherapy lines in improving survival of all patients with MBC warrants further study.