Tumor Lysis Syndrome (TLS) is a major oncological emergency involving metabolic perturbations. It occurs when tumor cells release their contents into the bloodstream, either spontaneously or in response to therapy. TLS is characterized by hyperuricemia, hyperkalemia, hyperphosphatemia and hypocalcemia following massive lysis of malignant cells. Although this syndrome is well described, it is rarely seen or suspected in solid malignancies. The frequency and severity of TLS is partly dependent upon the biology of the disease and type of therapy administered. We report in this work two cases of tumor lysis syndrome occurring after chemotherapy for endocrine colon carcinoma with small metastatic cells.