The role and indications for biopsy of a renal mass is controversial.
The aim of biopsy is to determine:
- Benign vs malignant
- Morphology – RCC or other
- Grade of RCC if able
Accepted and well-defined indications for biopsy:
- Indeterminate lesion suspected to not be RCC – i.e. metastasis, lymphoma, infective
- Prior to systemic treatment for RCC
Relative indications include:
- Bilateral renal masses
- Prior to focal therapy
Evolving or elective indications may include:
- Avoiding surgery in patients with benign tumours (accepting the issues associated with biopsy)
- Younger women are at higher risk of having a benign tumour
- EAU – “perform biopsy in select patients who are considering active surveillance”
Biopsy is not necessary in patients fit and willing for surgical treatment with a solid enhancing mass that looks like RCC.
Biopsy is not recommended for:
- Patients unfit or unwilling to undergo curative intent treatment
- Cystic masses
Regarding biopsy technique:
- Done under ultrasound or CT guidance
- Multiple passes with a 16 and 18 G core biopsy needle (better yield than FNA)
- Co-axial technique recommended (to reduce potential risk of seeding)
Potential morbidity:
- Bleeding – 5 % haematoma, 1 % transfusion
- Pain
- Pneumothorax
- Non diagnostic
- Tumour seeding – very rare – mostly reported prior to co-axial technique
Accuracy of renal biopsy:
- Non diagnostic in roughly 14 % of cases (a repeat biopsy is usually sufficient)
- Can be very difficult (some say impossible) to distinguish between oncocytoma and chromophobe RCC (esp eosinophilic variant)
- Difficult to assign grade – biopsied tissue may not be representative – often just graded as high or low – poor predictive value for high grade malignancy
- Positive predictive value > 99 % for malignancy
- Negative predictive value 63 – 80 % – therefore reasonably high rate of false negatives – usually chromophobe RCC / oncocytoma or sampling error