Nine weeks after a bilobectomy for stage IIIA N2 non‑small cell lung cancer, the patient's prostate‑specific antigen is 8 ng/mL; does this indicate metastatic lung cancer or a new primary prostate cancer?

Elevated PSA After Bilobectomy for Stage IIIA N2 NSCLC: Likely a New Primary Prostate Cancer

A PSA of 8.3 ng/mL nine weeks after bilobectomy for stage IIIA N2 NSCLC almost certainly represents a new primary prostate cancer rather than metastatic lung cancer, and requires immediate prostate biopsy for tissue diagnosis. 1

Why This is Not Metastatic Lung Cancer

• NSCLC rarely metastasizes to the prostate and does not produce PSA. Prostate-specific antigen is synthesized exclusively by prostatic epithelial cells, not by lung cancer cells. 2
• PSMA (prostate-specific membrane antigen) expression in NSCLC tumor cells occurs in only 6% of cases and is predominantly found in squamous cell carcinoma, not as a source of elevated serum PSA. 2
• Pulmonary metastases from prostate cancer are exceedingly rare; when they occur, they represent advanced disease with widespread metastases, not an isolated finding. 3
• The timing (9 weeks post-surgery) and PSA level (8.3 ng/mL) are inconsistent with any known mechanism by which lung cancer would elevate PSA. 1

Immediate Diagnostic Workup Required

Obtain prostate biopsy within 2-4 weeks. PSA values between 4-10 ng/mL represent intermediate risk with 50-70% probability of prostate cancer, and at 8.3 ng/mL the positive predictive value exceeds 50%. 1

• Perform multiparametric MRI of the prostate before biopsy to improve diagnostic yield and target sampling. 1
• Do not order a bone scan at this PSA level—AUA guidelines state bone scans are unnecessary when PSA < 20 ng/mL without high Gleason scores, as the likelihood of bone metastases at PSA 8.3 ng/mL is < 5%. 1
• Obtain contrast-enhanced CT of chest, abdomen, and pelvis to simultaneously monitor NSCLC status and evaluate for possible prostate cancer metastases if biopsy confirms malignancy. 1

Critical Pitfall to Avoid

Do not dismiss the elevated PSA as less important than the lung cancer. Both malignancies require appropriate evaluation, and delaying prostate biopsy could result in missed opportunity for curative treatment of a second primary cancer. 1

• The patient has already undergone definitive treatment for stage IIIA N2 NSCLC with bilobectomy (which carries 5-year survival of approximately 25-40% depending on complete resection and nodal downstaging). 4
• A newly diagnosed intermediate-risk prostate cancer at PSA 8.3 ng/mL is potentially curable with either radical prostatectomy or radiation therapy. 1

NSCLC Surveillance Must Continue

• Continue routine surveillance imaging for stage IIIA N2 NSCLC with chest CT every 3-6 months for the first 2 years post-treatment, as lung cancer carries markedly higher near-term mortality risk than newly diagnosed prostate cancer at this PSA level. 1
• Stage IIIA N2 disease represents a heterogeneous population with 5-year survival ranging from 7-40% depending on extent of nodal involvement, completeness of resection, and response to therapy. 4
• Bilobectomy after neoadjuvant chemoradiotherapy carries higher operative mortality (13% at 90 days) and poorer long-term survival compared to lobectomy. 5

Prostate Cancer Risk Stratification (If Confirmed)

If prostate biopsy confirms malignancy, the disease is most likely intermediate-risk based on PSA 8.3 ng/mL. 1

• Approximately 20% of men with PSA 2.6-10 ng/mL experience biochemical recurrence within 10 years after definitive therapy. 1
• Definitive treatment options include radical prostatectomy or external-beam radiation therapy combined with short-term androgen-deprivation therapy. 1
• Radiation therapy may be preferred over surgery in this patient who recently underwent thoracic surgery, to avoid additional surgical morbidity and prolonged recovery. 1

Timing of Prostate Cancer Treatment

Defer initiation of definitive prostate cancer therapy until the status of the lung cancer is clearly established (typically 3-6 months post-bilobectomy to assess for early recurrence). 1

• Treatment of one malignancy may compromise surveillance or therapy of the other. 1
• Androgen-deprivation therapy can be administered safely alongside ongoing lung cancer surveillance if prostate cancer treatment cannot be delayed. 1
• Coordinate follow-up among medical oncology (lung cancer), urology (prostate cancer), and radiation oncology to establish clear, joint surveillance protocols. 1

Monitoring Strategy

• If initial prostate biopsy is negative, repeat PSA testing in 3-6 months, as false-negative biopsies occur in 20-30% of cases. 1, 6
• Consider repeat biopsy if PSA continues to rise or if PSA velocity exceeds 0.75 ng/mL per year. 1, 6
• Use the same laboratory assay for longitudinal PSA monitoring, as variability between assays ranges from 20-25%. 6, 7