T1 tumours are ≤7 cm and limited to the kidney
T1a ≤4 cm
T1b >4 cm, but ≤7 cm
T2 tumours are >7 cm and also limited to the kidney
T2a >7 cm, but ≤10 cm
T2b >10 cm
T3 tumours are not limited to the kidney, and extend into the renal veins of IVC. They may extend into the perinephric fat without breaching Gerota's fascia.
T3a - tumour within perinephric fat, renal vein or segmental branches or invading the pelvicayceal system
T3b - tumour within IVC below the diaphragm
T3C - tumour within IVC above the diaphragm or in the IVC wall
T4 tumours breach Gerota's fascia or involve the adjacent adrenal gland

The regional lymph nodes of the kidney are defined in the AJCC Cancer Staging Manual(1) as:

Other nodes, not regional, are counted as metastases.

Roman numeral staging

Stage IV disease is any T4 or metastatic disease.

T1 to T4 tumours are all potentially resectable with radical nephrectomy the recommended treatment for T3 and T4 tumours(2). Nodal disease decreases the possibility of cure(3). Metastatectomy confers a survival benefit in selected patients(4-6) and is therefore recommended when appropriate(2). Palliative resection is also possible depending on performance status and even when there is metastatic disease, without metastectomy, nephrectomy is associated with a survival benefit(7,8).

References

1. M.B. Amin et al. (eds.), AJCC Cancer Staging Manual, Eighth Edition, DOI 10.1007/978-3-319-40618-3_60 Amin, Mahul B.. AJCC Cancer Staging Manual, Eighth Edition (p. 766-755). American College of Surgeons. Kindle Edition.
2. Ljungberg, B. et al. EAU Guidelines on Renal Cell Carcinoma: The 2010 Update. Eur. Urol. 58, 398–406 (2010).
3. Pantuck, A. J. et al. Renal cell carcinoma with retroperitoneal lymph nodes. Cancer 97, 2995–3002 (2003).
4. Kwak, C., Park, Y. H., Jeong, C. W., Lee, S. E. & Ku, J. H. Metastasectomy without systemic therapy in metastatic renal cell carcinoma: comparison with conservative treatment. Urol. Int. 79, 145–151 (2007).
5. Thyavihally, Y. B., Mahantshetty, U., Chamarajanagar, R. S., Raibhattanavar, S. G. & Tongaonkar, H. B. Management of renal cell carcinoma with solitary metastasis. World J. Surg. Oncol. 3, 48 (2005).
6. Brehmer, B., Piper, C., Pfister, D., Porres, D. & Heidenreich, A. [Metastasectomy for renal cell cancer]. Urol. Ausg 51, 1202–1208 (2012).
7. Flanigan, R. C. et al. Nephrectomy followed by interferon alfa-2b compared with interferon alfa-2b alone for metastatic renal-cell cancer. N. Engl. J. Med. 345, 1655–1659 (2001).
8. Mickisch, G. H., Garin, A., van Poppel, H., de Prijck, L. & Sylvester, R. Radical nephrectomy plus interferon-alfa-based immunotherapy compared with interferon alfa alone in metastatic renal-cell carcinoma: a randomised trial. Lancet 358, 966–970 (2001).