Over 90% of malignant kidney tumours are renal cell carcinoma — all adenocarcinomas, most arising from the proximal tubule (chromophobe, collecting duct, and medullary types are the exceptions). Subtype and grade drive prognosis, and the AJCC 8th-edition TNM system hinges on tumour size and venous/perinephric extension. The commonest benign renal tumours are oncocytoma and angiomyolipoma; RCC is also the most common renal tumour in pregnancy.
RCC Subtypes
| Subtype | Frequency | Origin / behaviour | Hallmark |
|---|---|---|---|
| Clear cell (ccRCC) | 70–80% | Proximal tubule; worst prognosis of the common types but most responsive to systemic therapy | VHL / 3p loss (VHL inactivated in 70–90%) |
| Papillary | 10–15% | Proximal tubule; often multifocal; common in ESRD/acquired cystic disease; type 1 better than type 2; systemic therapy ineffective | Trisomy 7/17, loss of Y; HPRCC (type 1), HLRCC (type 2) |
| Chromophobe | 3–5% | Distal tubule / collecting duct; generally good prognosis | Hale colloidal iron positive; Birt-Hogg-Dubé |
| Collecting duct | <1% | Collecting duct; poor prognosis; may respond to cisplatin/gemcitabine | Ulex europaeus lectin positive |
| Renal medullary | Rare | Collecting duct; dismal, often metastatic at diagnosis | Sickle cell trait (not disease); young African-Americans |
| Unclassified | 1–3% | Poorly differentiated, aggressive | — |
| Xp11.2 translocation / TFE3 | Rare | Children/young adults (40% of paediatric RCC); prognosis ≈ ccRCC | TFE3 gene fusion |
Multilocular cystic ccRCC behaves almost uniformly benignly, and papillary adenomas (≤5 mm) are benign look-alikes.
Other Histologic Features
- Sarcomatoid differentiation (1–5%) is not a subtype but an aggressive feature, most often seen with ccRCC or chromophobe — consider multimodal therapy.
- Cystic degeneration (10–25%) carries a better prognosis than purely solid RCC.
- Laterality/focality — most sporadic RCC is unilateral and unifocal; bilateral disease (2–4%) and multifocality (10–20%) are commoner with papillary histology and familial syndromes. Synchronous bilateral lesions are usually independent primaries, whereas asynchronous ones are usually metastases.
Grading
The Fuhrman system (1982) has been superseded by the ISUP/WHO grade (2012/2016), which uses more objective nuclear criteria. Grade 4 includes sarcomatoid/rhabdoid change, giant cells, and extreme pleomorphism. Chromophobe RCC is no longer graded. Higher grade tracks with larger, more aggressive tumours.
TNM Staging (AJCC 8th Edition)
| T stage | Definition |
|---|---|
| T1a / T1b | ≤4 cm / >4–7 cm, confined to the kidney |
| T2a / T2b | >7–10 cm / >10 cm, confined to the kidney |
| T3a | Renal vein or segmental branches, pelvicalyceal system, or perirenal/sinus fat (not beyond Gerota) — medial perisinus-fat invasion is worse than lateral perirenal |
| T3b | IVC below the diaphragm |
| T3c | IVC above the diaphragm, or invading the IVC wall |
| T4 | Beyond Gerota's fascia, including contiguous ipsilateral adrenal involvement |
N1 (regional nodes) carries a 5-year survival of 0–20%, and M1 (distant metastasis) 0–10%. Ipsilateral adrenal involvement is pT4 if by direct extension, otherwise pM1.
Self-Test
1. How does ccRCC prognosis compare with papillary and chromophobe, and which papillary type is better? ccRCC has a worse prognosis than papillary or chromophobe; type 1 papillary is better than type 2.
2. Which RCC develops more often in ESRD / acquired cystic disease? Papillary RCC.
3. Which RCC stains with Hale colloidal iron? Chromophobe.
4. Which RCC subtypes arise from the collecting duct? Chromophobe (distal tubule/collecting duct), collecting duct carcinoma, and renal medullary carcinoma — clear cell and papillary arise from the proximal tubule.
5. Outline the T-staging of RCC. T1 ≤7 cm (a ≤4, b >4–7) and T2 >7 cm (a ≤10, b >10), both confined; T3a renal vein/sinus fat, T3b IVC below the diaphragm, T3c IVC above the diaphragm or wall; T4 beyond Gerota's or ipsilateral adrenal.