Background: Head and neck squamous cell carcinoma (HNSCC) presents an ideal scenario for intratumoral therapies (IT), due to its local recurrence pattern and frequent superficial extension. IT therapies aim to effect tumor regression by directly injecting antineoplastic agents into lesions. However, there is a lack of updated evidence regarding IT therapies in HNSCC., Patients and Methods: A systematic literature search (CRD42023462291) was conducted using WebOfScience, ClinicalTrials.gov, and conference abstracts from ESMO and ASCO, identifying for IT clinical trials in patients with HNSCC, from database creation to September 12th, 2023. Efficacy as well as safety (grade ≥ 3 treatment-related adverse events[trAEs]) were reported., Results: After evaluation of 1180 articles identified by the systematic search, 31 studies treating 948 patients were included. IT injectables were categorized as chemotherapies with or without electroporation (k = 4, N = 268), oncolytic viruses, plasmids, and bacteria-based (k = 16, N = 446), immunotherapies and EGFR-based therapies (k = 5, N = 160), radioenhancer particles (k = 2, N = 68), and calcium electroporation (k = 1, n = 6). EGFR-antisense plasmids, NBTXR3 radioenhancer and immune innate agonists show best overall response rates, at 83 %, 81 % and 44 % respectively. Eleven (35 %) studies added systemic therapy or radiotherapy to the IT injections. No study used predictive biomarkers to guide patient selection. 97 % studies were phase I-II. Safety-wise, electroporation and epinephrine-based injectable trials had significant local symptoms such as necrosis, fistula formation and post-injection dysphagia. Treatment-related tumor haemorrhages of various grades were described in several trials. Grade ≥ 3 trAEs attributable to the other therapies mainly comprised general symptoms such as fatigue. There were 3 injectable-related deaths across the systematic review., Conclusion: This is the first review to summarize all available evidence of IT in HNSCC. As of today, IT therapies lack sufficient evidence to recommend their use in clinical practice. Continuing research on potential molecules, patient selection, safe administration of injections and controlled randomized trials are needed to assess their added benefit., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: PJL: research funding from Roche, Merck; speakerś bureau from MSD Merck Sharp & Dohme, travel and accommodation expenses from MSD, and Novartis; and stockholding from Elli Lilly outside the current work. AHC: travel and accommodation expenses from Merck Serono and Kyowa Kirin International and research grant from Gilead (Inst) outside the current work. IB received personal fees from Merck sharp & Dohme, Sanofi, Achilles Therapeutics, eTheRNA Immunotherapies, Cancer Expert Now, Boehringer Ingelheim as a Speakers’ Bureau: Bristol Myers Squibb, Merck Serono, Roche, MSD. Lastly, as a research Funding: AstraZeneca (Inst), Bristol Myers Squibb (Inst), Celgene (Inst), Gliknik (Inst), GlaxoSmithKline (Inst), Janssen Oncology (Inst), Kura Oncology (Inst), Merck Sharp & Dohme (Inst), Novartis (Inst), Pfizer (Inst), Roche (Inst), Shattuck labs (Inst), Nanobiotix (Inst), Seattle Genetics (Inst), Immutep (Inst), Debiopharm Group (Inst), Regeneron (Inst), Boehringer Ingelheim (Inst), ISA Pharmaceuticals (Inst), Merck Serono (Inst), Seattle Genetics (Inst), Northern Biologics (Inst), VCN Biosciences (Inst), and for travel, accommodations and expenses: MSD Oncology. VM: Consulting or Advisory Role: Roche (Inst), Bayer (Inst), Pieris (Inst), BMS (Inst), Janssen (Inst), Basilea (Inst), Regeneron/Sanofi (Inst), BMS (Inst), Bayer (Inst), Nanobiotix (Inst). Research Funding: AbbVie (Inst), Achilles (Inst), AbbVie (Inst), AceaBio (Inst), Adaptimmune (Inst), ADC Therapeutics (Inst), Arcus (Inst), Ascendis Pharma (Inst), Aduro (Inst), Agenus (Inst), Amcure (Inst), Amgen (Inst), Astellas (Inst), AstraZeneca (Inst), Bayer (Inst), Beigene (Inst), Biomea (Inst), BioInvent International AB (Inst), BMS (Inst), Boehringer (Inst), Boston Therapeutics (Inst), Celgene (Inst), Daiichi Sankyo (Inst), Debiopharm (Inst), Eisai (Inst), e-Terapeutics (Inst), Exelixis (Inst), Forma Therapeutics (Inst), Genmab (Inst), GSK (Inst), Harpoon (Inst), Hutchison (Inst), Immutep (Inst), Incyte (Inst), Inovio (Inst), Iovance (Inst), Janssen (Inst), Kyowa Kirin (Inst), Lilly (Inst), Loxo (Inst), Monta Bioscience (Inst), MedSir (Inst), Menarini (Inst), Merck (Inst), Merus (Inst), Millennium (Inst), MSD (Inst), Nanobiotix (Inst), Nektar (Inst), Novartis (Inst), Odonate Therapeutics (Inst), Pfizer (Inst), Pharma Mar (Inst), PharmaMar (Inst), Principia (Inst), PsiOxus (Inst), Puma (Inst), Regeneron (Inst), Relay Therapeutics (Inst), Revolution Medicines (Inst), Rigontec (Inst), Roche (Inst), Sanofi (Inst), Sierra Oncology (Inst), Synthon (Inst), Taiho (Inst), Takeda (Inst), Tesaro (Inst), Transgene (Inst), Turning Point Therapeutics (Inst), Upsher-Smith (Inst). BD: Principal Investigator – Institutional Funding: AbbVie, Achilles, AbbVie, AceaBio, Adaptimmune, ADC Therapeutics, Arcus, Ascendis Pharma, Aduro, Agenus, Amcure, Amgen, Astellas, AstraZeneca Bayer, Beigene, Biomea, BioInvent International AB, BMS, Boheringer, Boston Therapeutics, Celgene, Daichii Sankyo, Debiopharm, Eisai, e-Terapeutics, Exelisis, Forma Therapeutics, Genmab, GSK, Harpoon, Hutchison, Immutep, Incyte, Inovio, Iovance, Janssen, Kyowa Kirin, Lilly, Loxo, Monta Bioscience, MedSir, Menarini, Merck, Merus, Millennium, MSD, Nanobiotix, Nektar, Novartis, Odonate Therapeutics, Pfizer, Pharma Mar, PharmaMar, Principia, PsiOxus, Puma, Regeneron, Relay Therapeutics, Revolution Medicines, Rigontec, Roche, Sanofi, Sierra Oncology, Synthon, Taiho, Takeda, Tesaro, Transgene, Turning Point Therapeutics, Upshersmith. KJH received honoraria from Arch Oncology (Inst), AstraZeneca (Inst), BMS (Inst), Boehringer Ingelheim (Inst), Merck Serono (Inst), MSD (Inst), Oncolys Biopharma (Inst), Pfizer (Inst), Replimune (Inst), Inzen Therapeutics (Inst) and Codiak Biosciences (Inst). Consulting or Advisory Role: Arch Oncology (Inst), AstraZeneca (Inst), BMS (Inst), Boehringer Ingelheim (Inst), Merck Serono (Inst), MSD (Inst), Oncolys BioPharma (Inst), Replimune (Inst), Inzen Therapeutics (Inst) Speakers’ Bureau: BMS (Inst), Merck Serono (Inst), MSD (Inst) Research Funding: AstraZeneca (Inst), Merck Sharp & Dohme (Inst), Replimune (Inst), Boehringer Ingelheim (Inst). All other authors have declared no conflicts of interest., (Copyright © 2024. Published by Elsevier Ltd.)