A phase 1, open-label study to evaluate SGN-35C in adults with advanced malignancies.

Inclusion Criteria: - Tumor type - For dose escalation and back fill and dose optimization (Parts A and B): - Participants with a histologically confirmed lymphoid neoplasm who in the judgement of the investigator have no appropriate standard therapy available at the time of enrollment and are a candidate for PF-08046044/SGN- 35C treatment. Eligible subtypes and treatment status are as follows: - Participants with relapsed/refractory (R/R) cHL: should have received at least 3 prior systemic therapies including autologous stem cell transplant [ASCT] (ASCT and the associated high-dose chemotherapy prior to ASCT are considered to be 1 prior line, along with post-transplant consolidation if progression has not occurred between transplant and start of consolidation) or an anti-PD-1 agent (or refused/were ineligible); or 2 prior systemic therapies if, according to the investigator, no other appropriate standard treatment is available. - Participants with R/R PTCL (excluding systematic anaplastic large cell lymphoma [sALCL]): should have received at least 2 prior systemic therapies, or 1 prior systemic therapy if, according to the investigator, no other appropriate standard treatment is available. - Participants with R/R sALCL: should have received at least 2 prior systemic therapies, including 1 brentuximab vedotin-containing regimen, or 1 prior line of systemic therapy including brentuximab vedotin, cyclophosphamide, doxorubicin, and prednisone. - Participants with R/R DLBCL: should have received at least 2 prior systemic therapies, including ASCT and chimeric antigen receptor (CAR) T-cell therapy, or were ineligible, or refused. - Participants with PTCL and DLBCL must have a detectable cluster of differentiation 30 (CD30) expression level (≥1%) in tumor tissue from the most recent biopsy obtained at or after relapse by local testing. - For dose expansion (Part C): - Participants are eligible irrespective of CD30 expression on tumor tissue; however, participants must provide tumor tissue for evaluation of CD30 expression from the most recent biopsy obtained at or after relapse. - Participants with cHL, PTCL, sALCL, and DLBCL: Eligible subtypes are the same as defined in Parts A and B - If activated, the biology cohort may enroll the populations included in Parts A, B, and C. - Eastern Cooperative Oncology Group (ECOG) Performance Status score of ≤1 - Fluorodeoxyglucose positron emission tomography (FDG-PET) avid and bidimensional measurable disease as documented by radiographic technique (spiral computed tomography [CT] preferred) Exclusion Criteria: - Previous exposure to any antibody-drug conjugates (ADCs) with camptothecin-based payload. - History of another malignancy within 3 years before the first dose of study drug, or any evidence of residual disease from a previously diagnosed malignancy. Exceptions are malignancies with a negligible risk of metastasis or death - Active central nervous system (CNS) disease related to the underlying malignancy. Participants with a history of CNS disease related to the underlying malignancy are allowed if prior CNS disease has been treated and the participant is clinically stable (defined as not currently receiving steroid treatment for symptoms related to cerebral/meningeal disease and with no ongoing related AE). - Received previous ASCT infusion <12 weeks prior to the first dose of SGN-35C. - Previous allogeneic stem cell transplant (SCT) if they meet any of the following criteria: - <100 days from allogeneic SCT. Participants ≥100 days from allogeneic SCT who are stable without immunosuppressive therapy for at least 12 weeks are permitted. - Active acute or chronic graft-versus-host disease (GVHD) or receiving immunosuppressive therapy as treatment for or prophylaxis against GVHD. - History of clinically significant GI bleeding, intestinal obstruction, or GI perforation within 6 months of initiation of trial treatment.