Unknown Primary Cancer Presenting as Osteolytic Bone Lesion

Presentation

A 59-year-old male presents to an outpatient clinic with deep left groin pain for 2 months. He is a retired fireman with a past medical history of smoking for 10 years in his 20s, hypertension, and hypercholesterolemia. He reports that the left groin pain, which started without any incident or trauma, began as a dull achy pain but has become more intense and gets worse with activity. The patient denies any numbness or tingling of the left lower extremity, and he does not need to use any type of ambulatory assistive device.

Physical examination of the patient's left leg reveals normal contour of the left hip and hemipelvis and no gross deformity, overlying skin changes, evidence of erythema or ecchymosis or swelling, or palpable masses/nodules. Area is nontender to palpation, and there is no inguinal lymphadenopathy. Patient has good active and passive range of motion in the left hip. He walks with a slight antalgic gait to the left.

Workup and Diagnosis

X-rays of the patient’s left hip and pelvis reveal an osteolytic lesion of the superior dome of the left acetabulum. This finding is suspicious for possible metastatic bone disease in this age population. Because the patient does not have a history of cancer, the advanced practice provider (APP) orders a CBC with differential, electrolytes, sedimentation rate, C reactive protein, and alkaline phosphatase, as well as a serum protein electrophoresis, PSA, and urinalysis. Additional workup includes chest X-ray and CT of the chest/abdomen and pelvis, which reveals a mass on the left kidney suspicious for renal cell carcinoma, and whole body bone scan, which reveals increased uptake in the left acetabulum only. At this time, the suspected diagnosis is metastatic renal cell carcinoma.

Treatment

With the patient’s presenting symptoms and findings on imaging, it was determined that his suspected bone metastasis to the left acetabulum from renal cell carcinoma was weakening the bony structure enough to cause pain and put the patient at increased risk for a pathological fracture. The patient underwent internal fixation on his left acetabulum and a left total hip arthroplasty to help provide stabilization to his pelvis and diminish pain.

At the time of surgery, an interoperative biopsy of the left acetabulum was performed first to confirm the diagnosis of metastatic renal cell carcinoma. Once confirmed, the patient underwent extended curettage of the osteolytic bone metastasis of the superior dome of the left acetabulum with a left acetabular reconstruction using bone cement and a total hip arthroplasty.

Follow-Up

After a short hospital stay and three weeks of outpatient physical therapy, the patient’s incision is completely healed, he is ambulating with a walker and cane, and his pain has lessened. At this time, he is referred to GU oncology for treatment of his metastatic renal cell carcinoma and for consideration of external beam radiation to his left acetabulum.

Discussion

Three to 4% of all patients with metastatic bone disease have an unknown primary site.¹ Benign bone tumors are more common in the younger population, whereas malignant bone tumors, especially metastatic carcinomas that affect the bone, are much more common in individuals who are older than 40 years of age.² In a patient without a previous cancer history, this is considered a bone metastasis of unknown primary until proven otherwise.

The workup to find a primary malignancy includes a thorough history and physical, bloodwork, imaging, and biopsy. A CBC with differential and electrolytes are beneficial; sedimentation rate and C-reactive protein is needed to identify a possible infection; alkaline phosphatase is needed to quantify the amount of bone destruction; serum protein electrophoresis is needed to rule out multiple myeloma; a prostate-specific antigen (PSA) is needed to evaluate for prostate cancer; and a urinalysis is needed to look for gross and/or microscopic hematuria.

Imaging requires a chest x-ray and CT of the chest abdomen and pelvis to rule out a primary cancer of an internal organ. A total body bone scan is needed to evaluate the rest of the patient's skeleton to see if any other areas show increased uptake within the skeleton.

Eighty-five percent of unknown primaries are found with this workup for a primary malignancy.¹ Pathologic biopsy is ultimately needed to either make a diagnosis of the bone lesion or confirm a suspected diagnosis based on bloodwork and imaging.

References

1. Rougraff BT, Kneisl JS, Simon MA. Skeletal metastases of unknown origin. A prospective study of a diagnostic strategy. J Bone Joint Surg Am. 1993;75(9):1276-1281. doi:10.2106/00004623-199309000-00003
2. Biermann JS, Holt GE, Lewis VO, Schwartz HS, Yaszemski MJ. Metastatic bone disease: diagnosis, evaluation, and treatment. J Bone Joint Surg Am. 2009;91(6):1518-1530.