Antibiotic-Refractory Fever with Pyelonephritis-like Features Revealing Occult Metastatic High-Grade Serous Carcinoma: Competing Causes of Fever and Diagnostic Stewardship

Background and Clinical Significance: Occult malignancy is an easily missed cause of prolonged fever when urinary findings suggest pyelonephritis, and repeated empirical antibiotic courses can delay tissue diagnosis. We report such a case with competing explanations for fever. CasePresentation: A 62-year-old woman had six months of intermittent fever and one month of dysuria and right flank pain despite nine outpatient antimicrobial courses. On admission, her temperature reached 40.1 °C; she had pyuria with a non-diagnostic urine culture, para-aortic lymphadenopathy on computed tomography and negative blood cultures. Fever abated during intravenous flomoxef, recurred on the seventh day, persisted after its withdrawal and subsided by hospital day 16 before cancer-directed therapy. A single naproxen dose produced only transient defervescence. Nodal biopsy revealed metastatic high-grade serous carcinoma of the tubo-ovarian type (surgical–pathological FIGO stage IIIA1; clinical stage IVB on imaging, not histologically confirmed). The cause of fever remained undetermined; tumor-associated fever, a partially treated urinary infection and flomoxef-associated drug fever were possible contributors. Conclusions: When fever persists despite empirical antimicrobials and reassessment finds no convincing bacterial infection, clinicians should consider stopping rather than escalating antibiotics in stable, non-neutropenic patients under close monitoring, consider drug fever and other non-infectious causes, and pursue prompt tissue diagnosis.