Talimogene Laherparepvec with Pembrolizumab for Recurrent Metastatic Squamous Cell Carcinoma of the Head and Neck (MASTERKEY232 / KEYNOTE-137)MASTERKEY232

Inclusion Criteria - Male or female age ≥ 18 years at the time of informed consent - Histologically confirmed diagnosis of metastatic or recurrent SCCHN of the oral cavity, oropharynx, hypopharynx, or larynx. Disease must be unsuitable for curative surgical resection and must not be amenable to curative radiotherapy. - Disease must have progressed after treatment with a platinum-containing regimen and should be defined as one of the following: i. disease progression or recurrence between 3 to 6 months of prior curatively intended multimodal therapy (which includes platinum therapy) for locoregionally advanced SCCHN. ii. disease progression or recurrence after prior platinum therapy in the recurrent or metastatic setting Note: This criterion is only applicable for subjects who have not had treatment in the recurrent/metastatic setting - Subject must be candidate for intralesional therapy administration defined as one or more of the following: i. at least 1 injectable cutaneous, subcutaneous, or nodal SCCHN tumor ≥ 10 mm in longest diameter ii. multiple injectable cutaneous, subcutaneous, or nodal SCCHN tumors that in aggregate have a longest diameter of ≥ 10 mm Note: Mucosal surfaces of tumor lesions and visceral metastases should not be injected. - Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1 - Adequate organ function determined within 14 days prior to enrollment - Female subject of childbearing potential must have a negative pregnancy test within 72 hours prior to enrollment. - Other Inclusion Criteria May Apply Exclusion Criteria - Has known active central nervous system (CNS) metastases and/or carcinomatous meningitis. - Primary nasopharyngeal carcinoma. - Subject at risk of airway compromise in the event of postinjection tumor swelling/inflammation based on investigator judgment. - Phase 3: Previous treatment with 3 or more systemic regimens given for recurrent and/or metastatic disease - History of other malignancy within the past 3 years - History of interstitial lung disease (ILD). - Prior therapy with talimogene laherparepvec, pembrolizumab, other anti-PD-1, any other antibody or drug specifically targeting T-cell co-stimulation or immune check point pathway. - History or evidence of active autoimmune disease that has required systemic treatment in the past 2 years (ie, with use of disease modifying agents, corticosteroids or immunosuppressive drugs). - Evidence of clinically significant immunosuppression - Active herpetic skin lesions or prior complications of herpetic infection (eg, herpetic keratitis or encephalitis). - Requires intermittent or chronic treatment with an antiherpetic drug (eg, acyclovir), other than intermittent topical use. - Prior chemotherapy, radiotherapy, biological cancer therapy, targeted therapy, or major surgery within 28 days prior to enrollment or has not recovered to Common Terminology Criteria for Adverse Events (CTCAE) grade 1 or better from adverse event due to cancer therapy administered more than 28 days prior to enrollment. - Expected to require other cancer therapy while on study with the exception of local palliative radiation treatment to the site of bone and other metastasis. - Known human immunodeficiency virus (HIV) disease. - Has acute or chronic active hepatitis B virus or hepatitis C virus infection or received treatment with nucleotide analogs such as those used in the treatment of hepatitis B virus (eg, lamivudine, adefovir, tenofovir, telbivudine, entecavir), ribavirin, or interferon alpha within 12 weeks of initiation of study treatment. - Received live vaccine within 28 days prior to enrollment. - Subject is pregnant or breast-feeding, or expecting to conceive or father children within the duration of the trial - Female subject of childbearing potential or male subject of reproductive potential who is unwilling to use acceptable method(s) of effective contraception during study treatment and through 3 months after the last dose of talimogene laherparepvec/placebo or 4 months after the last dose of pembrolizumab, whichever is later. - Sexually active subjects or their partners unwilling to use male or female latex condom to avoid potential viral transmission during sexual contact while on treatment and within 30 days after treatment with talimogene laherparepvec/placebo. - Subject who is unwilling to minimize exposure with his/her blood or other body fluids to individuals who are at higher risks for herpes simplex virus type 1 (HSV-1)-induced complications (eg, immunosuppressed individuals, HIV-positive individuals, pregnant women, or children under the age of 1 year) during talimogene laherparepvec treatment and through 30 days after the last dose of talimogene laherparepvec - Has history of (non-infectious) pneumonitis that required steriods or current pneumonitis - Subjects with tumor that directly contacts or encases a major blood vessel AND there is ulceration and/or fungation onto the skin surface - History of re-irradiation to a field which includes the carotid arteries - Other Exclusion Criteria May Apply