Today, we’re looking into prostate cancer, specifically exploring the most common sites of metastasis and their anatomical relevance. Can you identify these locations and discuss the underlying reasons for their prevalence? Reflect on the anatomical pathways and structures involved in the spread of this disease. Strengthen your grasp of this critical aspect of oncology and enhance your clinical acumen regarding prostate cancer metastasis.
A 72-year-old man comes to the clinic for evaluation of lower back pain. The pain began four weeks ago, is present throughout the day, and awakens him at night. The patient does not have a history of recent trauma, weakness, or paraesthesias. He does not note any significant changes to the pain when standing or sitting. Past medical history is significant for hypertension. Medications include lisinopril and atorvastatin. The patient smokes 2-3 packs of cigarettes daily and has done so for 36 years. He does not use other recreational drugs or alcohol. Temperature is 37.0°C (98.6°F), pulse is 90/min, respirations are 20/min, and blood pressure is 120/75 mmHg. He is awake and oriented to time, place, and person. Tenderness is noted at the L1-L2 vertebral level. Examination of the external genitalia is non-contributory. Neurological examination reveals normal muscle strength and normal sensory findings. Rectal examination reveals an asymmetric non-tender nodule in the prostate. Straight leg raise testing is negative bilaterally.
Which of the following is likely to be found upon further evaluation?
A. Vertebral body compression fracture
B. Lumbar spinal stenosis
C. Osteolytic lesions in the lumbar spine
D. Lumbar disc herniation
E. Osteoblastic lesions in the lumbar spine
Scroll down for the correct answer!
The correct answer to today’s USMLE® Step 1 Question is…
E. Osteoblastic lesions in the lumbar spine
Before we get to the Main Explanation, let’s see why the answer wasn’t A, B, C, or D. Skip to the bottom if you want to see the correct answer right away!
Incorrect answer explanations
A. Vertebral body compression fracture
Incorrect: Compression fractures are often a complication of vertebral metastasis. This condition presents with acute lower back pain following falls or associated injury. This patient’s pain has been present for four weeks, and he has no associated trauma to the area.
B. Lumbar spinal stenosis
Incorrect: Spinal stenosis results from thickening of the ligamentum flavum and presents with insidious onset of low back pain and lower extremity weakness and numbness. Symptoms are often posture-dependent, with the extension of the spine aggravating the pain while spinal flexion relieves the pain. This patient’s pain is not affected by posture.
C. Osteolytic lesions in the lumbar spine
Incorrect: Osteolytic lesions are typical of myeloma, melanoma, non-small cell cancer of the lung, and non-Hodgkin lymphoma. Prostate cancer more commonly causes osteoblastic lesions.
D. Lumbar disc herniation
Incorrect: Disc herniation presents with lumbosacral radiculopathy (pain radiating below the knee) and lower back pain relieved with rest and aggravated with activity. Straight leg raise testing is often positive in these patients. This patient has no radiculopathy symptoms (e.g., radiating pain, paresthesias, weakness) and has a bilaterally negative straight leg test.
Main Explanation
The most common site for prostate cancer metastasis is the bone. Prostate cancer can lead to osteoblastic lesions in the lumbar spine. This patient presents with chronic back pain over the lumbar spine and an irregular nodule detected on DRE (digital rectal examination). These findings suggest underlying prostatic cancer with vertebral metastasis.
The prostate is a glandular fibromuscular organ that surrounds the prostatic urethra at the base of the bladder. Prostatic veins form a plexus surrounding the gland and subsequently drain into the vesical venous plexus and the internal iliac veins. Valveless communications between the prostatic and vertebral venous plexuses/Batson’s plexus pose a risk of vertebral metastasis in patients with underlying prostate cancer.
The most common manifestations of vertebral metastasis include insidious pain that develops over weeks to months. With prostate cancer, bony metastatic lesions are typically osteoblastic (sclerotic). DRE in patients with prostatic adenocarcinoma often reveals induration, asymmetry, or palpable nodules in the posterior and lateral aspects of the gland. Complications of vertebral metastasis include pathologic fractures, spinal cord compression (cauda equina syndrome), and neurological deficits. DRE is not considered a screening test for prostate cancer as it is neither sensitive nor specific; however, further investigation is required if abnormal findings are found on a DRE.
Major Takeaway
Prostatic veins contain valveless communications with the vertebral venous plexus–allowing for vertebral metastasis in patients with prostatic carcinoma, which presents with insidious, localized pain and osteoblastic lesions on imaging.
References
- Suva LJ, Washam C, Nicholas RW, Griffin RJ. Bone metastasis: mechanisms and therapeutic opportunities. Nat Rev Endocrinol. 2011 Apr;7(4):208-18. doi: 10.1038/nrendo.2010.227. Epub 2011 Jan 4. PMID: 21200394; PMCID: PMC3134309.
- Roodman GD. Mechanisms of bone metastasis. N Engl J Med. 2004 Apr 15;350(16):1655-64. doi: 10.1056/NEJMra030831. PMID: 15084698.
- Tateishi U, Morita S, Taguri M, Shizukuishi K, Minamimoto R, Kawaguchi M, Murano T, Terauchi T, Inoue T, Kim EE. A meta-analysis of (18)F-Fluoride positron emission tomography for assessment of metastatic bone tumor. Ann Nucl Med. 2010 Aug;24(7):523-31. doi: 10.1007/s12149-010-0393-7. Epub 2010 Jun 18. PMID: 20559896.
- Smith DS, Catalona WJ. Interexaminer variability of digital rectal examination in detecting prostate cancer. Urology. 1995 Jan;45(1):70-4. doi: 10.1016/s0090-4295(95)96812-1. PMID: 7529449.
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