Solitary Extramedullary Plasmacytoma With Development of T-cell Anaplastic Large-Cell Lymphoma: A Rare Case Report and Literature Review.

Solitary extramedullary plasmacytomas are an exceedingly rare form of malignant neoplasms characterized by a single localized mass located in any soft tissue that consists of abnormal plasma cells. This type of tumor is characterized by the absence of plasmacytosis on bone marrow biopsy, the absence of other lesions on imaging, and no clinical signs of multiple myeloma. They usually present with mass effect, so the clinical picture varies based on the location of the tumor. In cases where the tumor is located in the gastrointestinal tract, patients may experience abdominal pain, small bowel obstruction, or gastrointestinal bleeding. The diagnostic process typically involves imaging to identify the tumor and its location, followed by a biopsy of the lesion with subsequent immunohistochemical analysis, as well as fluorescence in situ hybridization, and finally, bone marrow biopsy. Treatment options vary depending on the tumor's location and may include radiation therapy, surgical resection, and chemotherapy. Currently, radiation therapy is the preferred first-line treatment, with the best outcomes reported in the literature. Surgery is also frequently used and is often followed by radiation therapy. While chemotherapy has not been shown to have significant benefits, the available data is insufficient, and further studies are required to make better conclusions. Disease progression is often associated with transformation to multiple myeloma, but due to the rarity of the disease, data is limited, and it remains unclear if other forms of progression exist.   We report a case of a 63-year-old male who presented to the hospital with symptoms of abdominal pain, nausea, and vomiting. A computed tomography scan revealed a mass causing bowel obstruction, which was subsequently resected and evaluated by pathology. The final diagnosis was determined to be a solitary extramedullary plasmacytoma. Since the margins of the resected mass were clear, the patient was managed with solely clinical observation. Approximately eight months later, the patient was diagnosed with T-cell anaplastic large-cell lymphoma, ultimately leading to his passing 15 months after the initial diagnosis of solitary extramedullary plasmacytoma. We present this case to increase awareness of the rare condition of solitary extramedullary plasmacytoma and to highlight the potential association with T-cell anaplastic large-cell lymphomas, as demonstrated in this patient's case. Given the possibility of malignant transformation, close monitoring is warranted in similar cases.