<br>        Inclusion Criteria:<br><br>          1. Male or female aged =18 years<br><br>          2. Participants with histologically or cytologically confirmed diagnosis of advanced or<br>             recurrent tumors (including lymphomas) for whom all standard treatments have been used<br>             or are not feasible and MK-4621 (RGT100) is a suitable treatment option and:<br><br>               1. For Group A: has cutaneous, sub-cutaneous (SC), or lymph node injectable tumors<br><br>               2. For Group B: has injectable liver tumors or liver metastases<br><br>          3. Eastern Cooperative Oncology Group (ECOG) performance status 0-2<br><br>          4. Life expectancy >3 months as assessed by the Investigator<br><br>          5. Adequate organ function<br><br>          6. Negative serum pregnancy test within 2 weeks before first dose of study drug if the<br>             participant is a woman of childbearing potential. Participants and participant's<br>             partners of childbearing potential must agree to use birth control consistently and<br>             correctly during the study and for at least 6 months after the last study drug<br>             application.<br><br>          7. At least 1 measurable lesion per Response Evaluation Criteria in Solid Tumors Version<br>             1.1 (RECIST 1.1) and 1 separate injectable lesion with diameter =1 cm but <7 cm<br><br>          8. Ability to provide written informed consent before any study drug-related screening<br>             procedures being performed<br><br>        Exclusion Criteria:<br><br>          1. Any tumor-directed therapy within 4 weeks before study treatment<br><br>          2. Treatment with investigational drugs within 4 weeks before study enrolment<br><br>          3. Systemic steroids at a dose of >10 mg of prednisolone, >2 mg of dexamethasone a day or<br>             equivalent, except topical (inhaled, topical, nasal) for the last 28 days and ongoing<br><br>          4. Participants with rapidly progressing disease (as determined by the Investigator)<br><br>          5. Ongoing immune-related adverse events (irAEs) and/or adverse events (AEs) = grade 2<br>             not resolved from previous therapies except vitiligo, stable neuropathy grade 2, hair<br>             loss, and stable endocrinopathies with substitutive hormone therapy<br><br>          6. Within 4 weeks of major surgery<br><br>          7. Prior splenectomy<br><br>          8. Documented history of active autoimmune disorders requiring systemic immunosuppressive<br>             therapy<br><br>          9. Primary or secondary immune deficiency<br><br>         10. Active allergy requiring systemic medication or active infections requiring<br>             anti-infectious therapy<br><br>         11. Seropositive (except after vaccination) for human immunodeficiency virus (HIV),<br>             hepatitis B virus (HBV) or hepatitis C virus (HCV)<br><br>         12. Clinically significant cardiac disease including heart failure (New York Heart<br>             Association, Class III or IV), pre-existing arrhythmia, uncontrolled angina pectoris,<br>             or myocardial infarction within 1 year before study entry<br><br>         13. Dementia or altered mental status that would prohibit informed consent<br><br>         14. Other severe, acute, or chronic medical or psychiatric condition or laboratory<br>             abnormality that may increase the risk associated with study assessed by the<br>             Investigator<br><br>         15. History of stroke, seizures, encephalitis, or multiple sclerosis<br><br>         16. Gastric ulcer or inflammatory bowel disease or Crohn's disease or ulcerative colitis<br>             in the last 6 months<br><br>         17. Active drug or alcohol abuse<br><br>         18. Pregnant or breast feeding<br>