Tumor lysis syndrome (TLS) is an oncologic emergency that is usually associated with hematologic malignancies either spontaneously or following early chemotherapy and is caused by massive tumor cell lysis. However, it has been rarely reported in solid tumors. We report a case of 25-year-old lady recently diagnosed with metastatic gastric adenocarcinoma who developed TLS after the fourth cycle of chemoimmunotherapy (FOLFOX plus Nivolumab). She presented with abdominal pain, decrease in oral intake and decreased urine output. Laboratory studies showed acute kidney injury with electrolyte disturbances and was diagnosed initially with autoimmune nephritis secondary to Nivolumab but was later found to have TLS and recovered after appropriate treatment. Soon after this complication, our patient was found to have disease progression on imaging which makes the incidence of TLS an indicator of disease progression.