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.