What is the appropriate management for a patient with a renal lesion that has slightly increased in size on CT compared to imaging performed two years ago?

Management of Growing Renal Lesion

For a renal lesion showing slight growth over 2 years, obtain a renal mass biopsy to confirm histology, then proceed with definitive treatment (partial nephrectomy or ablation for small masses <4 cm) if malignancy is confirmed, or continue active surveillance if benign or the patient has significant comorbidities.

Initial Assessment and Risk Stratification

The key issue here is that growth of a renal mass is a concerning sign for malignancy and typically warrants intervention rather than continued observation. The 2025 EAU guidelines establish that active surveillance is appropriate for small renal masses in elderly/comorbid patients, with mean growth rates around 3 mm/year being typical 1. However, growth beyond expected rates or any growth in younger, healthier patients should trigger action.

Critical Decision Points:

1. Characterize the lesion enhancement pattern:

• Obtain contrast-enhanced CT (if not already done) to assess enhancement
• Enhancement >10-20 Hounsfield units strongly suggests malignancy 2
• Lack of enhancement may indicate benign pathology, even with size increase 3

2. Obtain renal mass biopsy before proceeding:

• The 2025 EAU guidelines recommend biopsy before active surveillance, but only in patients for whom treatment will be considered if abnormal growth occurs 1
• Since your patient demonstrates growth, biopsy is now indicated to guide treatment decisions
• This avoids unnecessary surgery for benign lesions (which comprise 20-30% of small renal masses)

Treatment Algorithm Based on Lesion Size and Patient Factors

For Lesions ≤4 cm (cT1a):

If patient is surgical candidate:

• Partial nephrectomy remains gold standard for oncologic outcomes 1
• Ablative therapies (cryoablation for ≤4 cm, RFA for ≤3 cm) are appropriate alternatives for:
  • Elderly/comorbid patients unfit for surgery
  • Bilateral tumors or solitary kidney
  • Genetic predisposition to multiple tumors
  • Patient preference after informed consent about higher local recurrence rates 1

If patient has significant comorbidities or limited life expectancy:

• Continue active surveillance may be reasonable, as RCC-specific mortality is low compared to competing-cause mortality in this population 1
• However, documented growth shifts the risk-benefit calculation toward intervention in most cases

For Lesions >4 cm:

• Surgical intervention (partial or radical nephrectomy) is strongly recommended
• Ablative therapies should not be routinely offered 1

Common Pitfalls to Avoid

Do not continue surveillance indefinitely without tissue diagnosis when growth is documented. The 2025 EAU data shows progression to metastatic disease occurs in only 1-2% during surveillance 1, but this applies to stable lesions, not growing ones.

Do not assume all enhancing lesions require immediate surgery. Growth rate matters: slow growth (<3 mm/year) in elderly patients with comorbidities may still warrant continued observation 4, but faster growth or growth in younger patients demands action.

Do not skip biopsy in favor of empiric treatment unless the clinical scenario clearly indicates surgery regardless of histology. Approximately 20-30% of small renal masses are benign, and biopsy technique has improved substantially 5.

Surveillance Protocol If Continuing Observation

If biopsy shows benign pathology or patient/physician elect continued surveillance despite growth:

• Imaging schedule: CT/MRI at 3 and 6 months, then every 6 months up to 3 years, then annually 1
• Intervention triggers: Continued growth, development of symptoms, or patient preference change
• Use contrast-enhanced imaging to monitor for enhancement patterns suggesting malignant transformation

The evidence strongly supports that any documented growth in a renal mass warrants either tissue diagnosis or definitive treatment, particularly in patients who are reasonable surgical candidates. The days of indefinite observation for growing renal masses have passed with improved understanding of natural history and better minimally invasive treatment options.