Tumor lysis syndrome following letrozole for locally advanced breast cancer: a case report.

Background: Letrozole, an aromatase inhibitor, is used to treat breast cancer in postmenopausal women. Tumor lysis syndrome (TLS) is a complication that can trigger multiple organ failure caused by the release of intracellular nucleic acids, phosphate, and potassium into the blood due to rapid tumor cell disintegration induced by drug therapy. TLS is uncommon in solid tumors and occurs primarily in patients receiving chemotherapy. Herein, we report a rare occurrence of TLS that developed in a patient with locally advanced breast cancer following treatment with letrozole.

Case Presentation: An 80-year-old woman with increased bleeding from a fist-sized left-sided breast mass presented to our hospital. Histological examination led to a diagnosis of invasive ductal carcinoma of the luminal type. The patient refused chemotherapy and was administered hormonal therapy with letrozole. Seven days after letrozole initiation, she complained of anorexia and diarrhea. Blood test results revealed elevated blood urea nitrogen (BUN) and creatinine (Cr) levels, and she was admitted to our hospital for intravenous infusions. On the second day after admission, marked elevations of LDH, BUN, Cr, potassium, calcium, and uric acid levels were observed. Furthermore, metabolic acidosis and prolonged coagulation capacity were observed. We suspected TLS and discontinued letrozole, and the patient was treated with hydration, febuxostat, and maintenance hemodialysis. On the third day after admission, her respiratory status worsened because of acute respiratory distress syndrome associated with hypercytokinemia, and she was intubated. On the fourth day after admission, her general condition did not improve, and she died.

Conclusions: Although TLS typically occurs after chemotherapy initiation, the findings from the present case confirm that this syndrome can also occur after hormonal therapy initiation and should be treated with caution.