Inclusion Criteria

   - Newly diagnosed PTCL, excluding systemic anaplastic large cell lymphoma (sALCL), per
   the Revised European-American Lymphoma World Health Organization (WHO) 2016
   classification

   - The following non-sALCL PTCL subtypes are eligible:

      - PTCL - not otherwise specified (PTCL-NOS)

      - Angioimmunoblastic T-cell lymphoma (AITL)

      - Adult T-cell leukemia/lymphoma (ATLL; acute and lymphoma types only, must be
      positive for human T cell leukemia virus 1)

      - Enteropathy-associated T-cell lymphoma (EATL)

      - Hepatosplenic T-cell lymphoma

      - Monomorphic epitheliotropic intestinal T-cell lymphoma (MEITCL)

      - Indolent T-cell lymphoproliferative disorder (T-LPD) of the gastrointestinal (GI)
      tract

      - Follicular T-cell lymphoma

      - Nodal peripheral T-cell lymphoma with T-follicular helper (TFH) phenotype

   - CD30 expression <10% by local assessment in tumor containing lymph node or other
   extranodal soft tissue biopsy

   - Fluorodeoxyglucose (FDG)-avid disease by PET and measurable disease of at least 1.5 cm
   by CT, as assessed by the site radiologist

   - An Eastern Cooperative Oncology Group (ECOG) performance status less than or equal to
   2

Exclusion Criteria

   - Current diagnosis of any of the following:

      - sALCL

      - Primary cutaneous T-cell lymphoproliferative disorders and lymphomas

      - Mycosis fungoides (MF), including transformed MF

   - History of another primary invasive cancer, hematologic malignancy, or myelodysplastic
   syndrome that has not been in remission for at least 3 years. Exceptions are
   malignancies with a negligible risk of metastasis or death (e.g., 5-year OS ≥90%),
   such as carcinoma in situ of the cervix, non-melanoma skin carcinoma, localized
   prostate cancer, ductal carcinoma in situ, or Stage I uterine cancer.

   - History of progressive multifocal leukoencephalopathy (PML).

   - Cerebral/meningeal disease related to the underlying malignancy.

   - Prior treatment with brentuximab vedotin or doxorubicin.

   - Baseline peripheral neuropathy Grade 2 or higher (per the NCI CTCAE, Version 4.03) or
   subjects with the demyelinating form of Charcot-Marie-Tooth syndrome.

   - Left ventricular ejection fraction less than 45% or symptomatic cardiac disease
   (including symptomatic ventricular dysfunction, symptomatic coronary artery disease,
   and symptomatic arrhythmias), or myocardial infarction within the past 6 months, or
   previous treatment with complete cumulative dose of >300 mg/m2 of doxorubicin.

   - Any uncontrolled Grade 3 or higher (per the National Cancer Institute's Common
   Terminology Criteria for Adverse Events, NCI CTCAE Version 4.03) viral, bacterial, or
   fungal infection within 2 weeks prior to the first dose of study drug. Routine
   antimicrobial prophylaxis is permitted.