Ph1 Study of SL-172154 Administered Intratumorally in Subjects With Squamous Cell Carcinoma of the Head and Neck or Skin

Inclusion Criteria: Participants are eligible to be included in the study only if all the following criteria apply: * Subject has voluntarily agreed to participate by giving written informed consent in accordance with ICH/GCP guidelines and applicable local regulations. * Subject must have a histologically confirmed diagnosis of an unresectable or recurrent, locally advanced or metastatic cutaneous squamous cell carcinoma or squamous cell carcinoma of the head and neck that is not amenable to curative surgery or radiotherapy. * Subjects must have received, been intolerant to, or ineligible for standard therapy(ies) known to provide clinical benefit for their condition. * Subject has measurable disease by RECIST v1.1 using radiologic assessment. * Subject has at least 1 tumor lesion measuring between 1-6cm that is cutaneous and/or subcutaneous and/or nodal and is clinically accessible and safe for injection by direct visualization, palpation or by ultrasound guidance. PD Cohort Subjects Only: Must have a second lesion that is non-injected and is amenable to tumor biopsy collection. * Subject age is 18 years and older. * Subject has an Eastern Cooperative Oncology Group (ECOG) Performance Status of 0 or 1. * Has life expectancy of greater than 12 weeks. * Has adequate organ function. * Females of childbearing potential (FCBP) must have a negative serum or urine pregnancy test within 72 hours of D1 of IP. * Male subjects of reproductive potential must use acceptable contracept…