Inappropriate treatment of prostate cancer caused by heterophilic antibody interference

Background A 58-year-old man, without any personal or familial risk factors for prostate cancer, visited his primary care physician for a first routine prostate cancer screening with a serum PSA test. Investigations Serum PSA test, digital rectal examination, prostate biopsy and pathological analysis, repeat serum PSA tests and pathological re-evaluation, abdominal tomodensitometry, whole-body bone scan and prostatic MRI. Diagnosis Highly elevated serum PSA indicative of advanced prostate cancer at high risk for metastasis. Management The patient was started on androgen deprivation therapy with goserelin acetate and bicalutamide. At 3 months, he was asymptomatic, his prostate was atrophic on digital rectal examination and he had suppressed serum testosterone. However, his serum PSA level remained highly elevated in the absence of any radiographic evidence of advanced cancer. A repeat PSA test using a different assay returned a negligible PSA concentration; evaluation with blocker agents revealed the presence of heterophilic antibody interference with the original PSA assay. The patient was rediagnosed as having a likely low-grade prostate adenocarcinoma; androgen deprivation therapy was stopped, and he was deemed a candidate for watchful waiting. At 15 months, his serum PSA level remained stable at a low level, and prostatic dynamic MRI showed no sign of tumor in the prostate or in the pelvis.