Synchronous colorectal cancer and multiple myeloma with chest wall involvement: Is this a coincidence?

Multiple primary malignant neoplasms (MPMNs) are rare malignant neoplasms that simultaneously or successively occur in the same patient as 2 or more primary malignancies. Currently, an increasing number of cases are being reported. In general, MPMNs more commonly occur as 2 solid tumors or 2 hematological malignancies. Cases of MPMN that involve a solid tumor and a hematological malignancy are rare. Here, we report a case of synchronous colorectal cancer (CRC) and multiple myeloma (MM) with chest wall involvement. After reviewing the literature, we believe that there may be a distinct syndrome involving CRC and MM. The patient in our case study suffered refractory anemia following surgery and 2 cycles of chemotherapy. Initially, the anemia was considered to be a common manifestation of CRC in this patient. Interestingly, although he received a blood transfusion, his hemoglobin levels remained low. He later developed hematuria, proteinuria, multiple osteoporosis in the costal bones, and thrombocytopenia. These new symptoms drew our attention, and we considered a diagnosis of synchronous primary CRC and MM, with the anemia as a symptom of MM. Based on the results of a bone marrow aspirate, MM was confirmed. Therefore, when CRC is associated with refractory anemia, we should not only assume that anemia is a classical symptom of CRC, a result of chronic blood loss, nutritional deficiencies, or myelosuppression due to chemotherapy, but we should also consider that it may reflect the possibility of a coexisting hematologic malignancy. As the treatment of these 2 malignancies is different, early diagnosis and treatment based on definitive diagnosis as early as possible will be beneficial to overall prognosis.