Leser-Trélat Sign as an Initial Manifestation of Synchronous Prostate and Bladder Cancer.

The Leser-Trélat sign, marked by the sudden onset and rapid proliferation of seborrheic keratoses, is a rare paraneoplastic phenomenon associated with internal malignancies. This report presents a case of a 75-year-old male with a history of hypertension and diabetes who presented with an elevated PSA level and was subsequently diagnosed with synchronous prostate adenocarcinoma and high-grade invasive urothelial carcinoma. Prior to the oncologic diagnoses, the patient exhibited cutaneous lesions consistent with the Leser-Trélat sign, which raised clinical suspicion for an underlying malignancy. The patient's treatment course comprised transurethral resection of the bladder tumor, complete intravesical Bacillus Calmette-Guérin therapy, radical prostatectomy, and subsequent combined androgen deprivation therapy with salvage radiotherapy due to persistent postoperative PSA elevation. The stabilization of the patient's dermatologic manifestations following oncologic treatment supports the hypothesis of a paraneoplastic origin. The Leser-Trélat sign, while infrequent and debated, may serve as an early indicator of malignancy, particularly when observed with atypical seborrheic keratosis distribution. Although the pathogenesis remains incompletely understood, molecular associations such as FGFR3 mutations have been implicated. The co-occurrence of this sign with synchronous genitourinary malignancies underscores the importance of a multidisciplinary approach to diagnosis and management. Further investigation is warranted to elucidate the precise underlying mechanisms of this rare phenomenon and its potential role in oncologic detection.