Stage IV Prostate Cancer Presenting With a Low Prostate-Specific Antigen Level: A Case Report.

Prostate cancer is one of the most common cancers diagnosed in men and is typically monitored through prostate-specific antigen (PSA) levels. Metastatic prostate cancer usually presents with elevated PSA levels. However, a minority of these patients have low to minimal elevation. Here, we describe the case of a 70-year-old male with a history of essential hypertension and hypertriglyceridemia who presented to the emergency department after a fall, which ultimately revealed lytic spinal lesions on computed tomography. The lesions raised the concern for possible malignancy, possible osteoporotic fractures, or multiple myeloma. Additional investigation, including a biopsy, yielded no definitive diagnosis. Notably, the patient's PSA was 3.42 ng/mL following the non-diagnostic biopsy. Over the proceeding months, the patient developed progressively worsening weight loss and confusion. He presented to the emergency department a second time for this confusion and had a witnessed seizure. A second biopsy confirmed prostate cancer. A follow-up positron emission tomography scan further confirmed stage IV prostate carcinoma. This case highlights the complexity of prostate cancer in the face of low to mildly elevated PSA. Biological variability in prostate tumors, including the possibility of subclones that produce minimal PSA, can delay diagnosis. The patient, in this case, was started on a regimen of androgen deprivation therapy combined with abiraterone and prednisone. Clinicians should maintain a high index of suspicion for prostate cancer, especially in patients with unexplained skeletal lesions, regardless of PSA level. Clinicians should promptly perform further histopathological assessment and advanced imaging to ensure timely diagnosis and treatment.