Flare and tumor lysis syndrome with atypical features after letrozole therapy in advanced breast cancer. A case report.

Tumor lysis syndrome, which develops after effective therapy of malignant conditions and leads to hyperuricemia, hyperkaliemia, hyperphosphatemia, hypocalcemia and elevated lactate dehydrogenase, is uncommon in solid tumors. In breast carcinoma it can be associated with tamoxifen flare, i.e. a transient increase in symptoms, mainly bone pain, observed shortly after the start of tamoxifen therapy. We report the case of a patient with advanced breast carcinoma involving the pleural space, unresponsive to combined chemotherapy, who experienced rapid worsening after the initiation of letrozole. Her symptoms included shock, bilateral pleural effusion, cardiac tamponade and oliguria. Laboratory parameters disclosed elevated transaminase, lactate dehydrogenase, uric acid and D-dimer blood levels. The patient was in critical condition for nearly 2 weeks. She improved progressively and has remained well and in complete remission for 20 months. This clinical picture suggests increased damage to the pleura (and probably the pericardium) and rapid leakage of tumor products, following the start of endocrine therapy. Letrozole is a non-steroidal aromatase inhibitor which is used in advanced breast cancer, resistant to first-line endocrine/chemotherapeutic treatment. Our review of the literature did not disclose any other descriptions of flare and tumor lysis syndrome after aromatase inhibitor therapy. Moreover, this case was characterized by atypical and complex clinical features. The aim of this presentation is to point out the practical significance, in neoplastic patients, of the differential diagnosis between symptoms due to tumor progression and those associated with anomalous reactions to therapy.