**Author details**

depending on the type of drug tested, being most useful in the case of sorafenib (which

**Modified Choi criteria** evaluate existing changes in both size and tumor density after treat‐ ment. These criteria could differentiate those patients at risk of disease progression, but

**SACT criteria** (Size and Attenuation CT) differ from the modified Choi criteria that estab‐ lish an absolute value of change in tumor density (> 20 UH) rather than a % of change. These criteria are more reliable in the case of low attenuation pre-therapy lesions, in which it is

Finally, the **MASS criteria** (Morphology, Attenuation, Size, and Structure) include morpho‐ logical and structural elements regardless of the size and density of lesions. These criteria are intended to take into account the extensive necrotic changes frequently associated with

However, both SACT as MASS criteria are complicated and basically useful in differentiat‐ ing patients with a long progression-free survival (> 250 days) of those showing a rapid pro‐ gression (<250 days). Overall, we consider that in all these criteria contrast enhancement of lesions plays a major role, so that both imaging protocols (volume of contrast acquisition phase, etc.) or factors such as cardiac function patient can significantly influence the results.

The era of molecular biology have created great expectations on our ability to translate these discoveries into effective treatments for patients. Over the last decade, there has been an in‐ creasing knowledge about pathophysiological processes that are common to most tumors including: independence from growth signals, insensitivity to growth-inhibitory signals, evasion of apoptosis, limitless potential for replication, sustained angiogenesis, and tissue invasion and metastasis. These major pathways deregulated in cancer have a key role in tu‐ mor development and microenvironment. These features have enabled the emergence of a wide spectrum of novel oncologic drugs that are designed to target and interfere with spe‐ cific aberrant biological pathways. In general, these agents use different strategies to inter‐ fere with specific biological targets, such as blocking growth factors, receptors, or tyrosine

The use of new drugs in the treatment of advanced or metastatic kidney cancer, with differ‐ ent mechanisms of action compared to conventional chemotherapy raises new questions. One of the biggest problems with new drugs are produced in the evaluation of the response, and the incorporation of new imaging techniques (MRI diffusion, perfusion CT, nuclear

In this chapter we have reviewed the main techniques of radiological diagnosis and staging, the value of new imaging modalities, and discuss the validity of the classical criteria of inter‐

medicine, etc....) in the diagnosis of extension and assessment of efficacy.

tends to cause more degree of necrosis in lesions) than for sunitinib.

shows a tendency to classify patients as responders.

easier to obtain a percentage decrease in density.

tumor response to these drugs [63].

**6. Summary**

62 Renal Tumor

kinase (TK) action.

pretation of response.

