CIM Case: Metastatic Renal Cell Carcinoma to Humerus

Clinical Scenario

Patient: 58-year-old man Presentation: Progressive left arm pain for 8 weeks, now with difficulty lifting objects, pain at night disturbing sleep Relevant history: Renal cell carcinoma diagnosed 2 years ago (right nephrectomy, clear cell type, T3aN0M0 at diagnosis), recent surveillance CT showed no recurrence in renal bed, no prior chemotherapy, otherwise well, smoker (20 pack-years), no other medical history Examination findings:

• Well-appearing man, no cachexia
• Tender mass palpable over mid-left humerus (firm, fixed to bone)
• Overlying skin normal, warm to touch
• Full shoulder and elbow range of motion (limited by pain)
• No wasting of deltoid or arm muscles
• Neurovascularly intact distally (radial pulse normal)
• Lungs clear on auscultation
• Abdomen soft, left nephrectomy scar healed

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Investigations Provided

Laboratory Results

Imaging

Image 1: AP and Lateral Radiographs of Left Humerus

Radiological features:

• Large lytic lesion in mid-diaphysis of humerus
• Geographic destruction with moth-eaten margins
• Cortical erosion (>50% circumference involved)
• No matrix mineralisation
• Soft tissue mass visible extending from bone
• No periosteal reaction
• No pathological fracture yet
• Lesion spans approximately 8cm longitudinally

Image 2: CT Chest/Abdomen/Pelvis (Staging)

Findings:

• Right nephrectomy (known)
• No renal bed recurrence
• No liver metastases
• Solitary 5mm pulmonary nodule in right lower lobe (indeterminate)
• No other bone lesions on CT
• No lymphadenopathy

Image 3: Bone Scan (Whole Body)

Findings:

• Hot lesion in mid-left humerus
• Cold centre (photopenic) with hot rim
• No other skeletal lesions
• Normal uptake in kidneys/bladder

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Questions & Model Answers

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Key Teaching Points

Pattern Recognition

This pattern suggests Renal Cell Carcinoma Bone Metastasis:

• History of RCC (even remote)
• Lytic, expansile bone lesion
• Hypercalcaemia
• Hypervascular appearance on imaging
• Hot lesion with cold centre on bone scan (vascular tumour necrosis)
• Late presentation (years after primary)

Lytic Bone Metastases Mnemonic: "Lots of Trouble Kills Patients Badly":

• Lung
• Thyroid
• Kidney
• Prostate (usually blastic, can be lytic)
• Breast

Critical Management Points

1. Confirm solitary - PET-CT before planning curative surgery
2. Preoperative embolisation - ESSENTIAL for RCC (highly vascular)
3. Mirels score ≥9 - prophylactic fixation indicated
4. Wide excision for curative intent - if truly solitary, 2-3cm margins
5. MDT approach - oncology, orthopaedics, IR, radiology
6. Bone-modifying agents - reduce skeletal events
7. Long-term surveillance - RCC can recur late

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Common Examiner Follow-ups

Q: "What is the 'cold in hot' sign on bone scan and what does it indicate?"

The "cold in hot" or "doughnut" sign:

• Peripheral hot rim with central photopenic (cold) area
• Indicates highly vascular tumour with central necrosis
• Classic for renal cell carcinoma metastases
• Also seen in aggressive vascular tumours

Mechanism: The centre has outgrown its blood supply leading to necrosis, while the periphery remains hypervascular and metabolically active.

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Q: "Why is RCC relatively radioresistant and what are the implications?"

RCC is considered radioresistant because:

• Conventional fractionated RT has limited efficacy
• May relate to hypoxic tumour microenvironment
• VHL pathway mutations affect hypoxia response

Implications:

• Surgery preferred for local control when feasible
• Stereotactic body radiotherapy (SBRT) more effective (high dose per fraction)
• Radiotherapy alone not reliable for local control
• Post-operative RT role is limited

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Q: "How do you manage the 5mm lung nodule?"

Management of indeterminate lung nodule:

• Repeat CT in 3-6 months (Fleischner Society guidelines)
• If stable for 2 years: likely benign
• If growing: biopsy or resection
• PET-CT has limited sensitivity for lesions <8mm
• Changes surgical plan if proven metastatic (no longer solitary)

For this patient:

• If nodule is stable/benign: proceed with curative resection of humerus
• If nodule is metastatic: palliative approach more appropriate

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Q: "What are the indications for amputation in this scenario?"

Amputation indications for bone metastasis (rare):

• Massive neurovascular involvement not reconstructable
• Failed limb salvage with infection
• Uncontrollable haemorrhage
• Fungating tumour with skin breakdown
• Patient preference after informed discussion

For this patient with localised disease, limb salvage should be achievable with modern techniques.

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Related Topics

• Pathological Fractures
• Mirels Scoring System
• Preoperative Embolisation
• Endoprosthetic Reconstruction
• Bone Metastasis Management
• Immunotherapy in Oncology