Learning objectives
By the end of this lesson, the resident should be able to understand the epidemiological importance of renal cell carcinoma, recognize its main risk factors and histological subtypes, interpret the fundamental molecular basis of clear cell carcinoma, and relate these biological mechanisms to clinical behavior and current therapeutic strategies.
Renal cell carcinoma (RCC) is the most important malignant neoplasm arising from the renal parenchyma and accounts for approximately 90% of malignant kidney tumors in adults. It is not a single disease, but a heterogeneous group of tumors with different histological, molecular, prognostic, and therapeutic characteristics.
This heterogeneity is particularly important for the urologist. Today, when faced with a renal mass, it is not enough to ask whether the lesion is malignant. We must also consider its size, radiological features, probable histology, aggressiveness, extent, patient characteristics, and the possibilities for renal preservation.
Knowledge of molecular biology has also changed our understanding of kidney cancer. Alterations such as inactivation of the VHL gene and the resulting activation of HIF- and VEGF-related pathways help explain, at least in part, the marked angiogenic behavior of clear cell renal carcinoma and form the biological basis of several systemic treatments.
Key concept
Renal carcinoma should be understood as a heterogeneous group of diseases with different biology and clinical behavior.
Renal cell carcinoma is a relevant oncological problem worldwide. According to the data included in this material, GLOBOCAN 2022 recorded 434,840 new cases and 155,953 deaths from this disease. In addition, demographic projections estimate a considerable increase in its incidence over the coming decades.
The disease is more frequent in men than in women, with an approximate ratio of 1.7:1, and its peak incidence is between the sixth and seventh decades of life. There are also important geographic differences, with historically higher incidence in Northern Europe, North America, and Australia.
Over recent decades there has been a sustained rise in the diagnosis of kidney cancer. One of the main explanations is the increasingly frequent use of abdominal imaging for reasons unrelated to kidney disease.
Ultrasounds, CT scans, and MRIs ordered for other reasons can detect small renal masses in completely asymptomatic patients. This phenomenon has profoundly changed how kidney cancer presents and explains why a considerable proportion of these tumors are now diagnosed incidentally.
However, the rise in incidence does not seem to be explained solely by greater use of imaging. An increase in modifiable risk factors, especially obesity and hypertension, has also been observed.
Clinical pearl
The resident should incorporate the concept of the incidental renal mass. Today, kidney cancer often begins as a radiological finding rather than as a patient presenting with urological symptoms.
RCC comprises different histopathological entities. The main subtypes described in the material are:
| Subtype | Approximate frequency |
|---|---|
| Clear cell carcinoma | 70–80% |
| Papillary carcinoma | 10–15% |
| Chromophobe carcinoma | 5% |
| Other subtypes | Less common |
This classification matters beyond pathology. The different subtypes have distinct molecular alterations and may differ in clinical course, prognosis, and response to treatment.
Clear cell carcinomaClear cell renal carcinoma, or ccRCC, is the predominant subtype, and for that reason much of the molecular knowledge and many of the systemic treatments for kidney cancer have been developed around this entity. Its characteristic gross appearance and marked vascularity are related to its cellular composition and, especially, to its particular molecular biology.
Papillary carcinomaIt accounts for approximately 10–15% of renal carcinomas according to the source material. It is a biologically distinct entity from clear cell carcinoma and should be recognized as such.
Chromophobe carcinomaIt accounts for approximately 5% of renal carcinomas and is another subtype with particular histological and molecular characteristics.
Key concept
Not all renal carcinomas are clear cell carcinomas. Histology provides biological, prognostic, and therapeutic information.
One of the fundamental concepts for understanding the biology of ccRCC is the VHL–HIF pathway.
The VHL (Von Hippel-Lindau) gene is a tumor suppressor gene located on chromosome 3p25. The thesis material describes its inactivation, through somatic mutation, deletion, or promoter methylation, in a high proportion of sporadic clear cell renal carcinomas.
What happens when VHL is lost?Under normal conditions, the VHL protein takes part in the regulation and degradation of the hypoxia-inducible factors, known as HIF.
When VHL loses its function, HIF-1α and HIF-2α are no longer properly degraded even when oxygen concentration is normal.
As a result, the tumor cell behaves, at the molecular level, as if it were in a hypoxic environment. This phenomenon is called pseudohypoxia.
The accumulation of HIF subsequently activates the expression of various molecules, including:
The result is a particularly angiogenic and metabolically active phenotype.
Conceptual sequenceLoss of VHL → accumulation of HIF → pseudohypoxia → increased VEGF and other signals → angiogenesis and tumor progression.
This sequence connects molecular biology with clinical practice.
The marked angiogenic component of ccRCC is one of the rational bases for developing treatments targeting VEGF-related pathways.
Clinical pearl for residents
Do not memorize VHL, HIF, and VEGF as three independent names. Understand them as parts of a single biological pathway.
Although VHL is a central alteration, it does not by itself explain the entire behavior of clear cell renal carcinoma. Other relevant genetic alterations exist.
PBRM1It is one of the genes most frequently altered in ccRCC. The material describes mutations in approximately 45% of cases and notes their association with specific prognostic features.
BAP1BAP1 mutations are described in approximately 10–15% of cases and are associated with features of greater aggressiveness, including higher histological grade and tumor necrosis.
SETD2Somatic alterations of SETD2 are also found in a proportion of clear cell carcinomas.
This genetic diversity helps explain why two tumors that look similar from an anatomical standpoint can show different biological behavior.
Key concept
Even within clear cell carcinoma there is marked molecular heterogeneity.
Clear cell renal carcinoma shows substantial metabolic reprogramming.
One of its characteristics is the use of aerobic glycolysis, a phenomenon known as the Warburg effect. This produces lactate and helps create an acidic tumor microenvironment that can promote mechanisms of invasion and immune escape.
There are also important changes in lipid metabolism. Tumor cells increase fatty acid uptake and synthesis to meet their energetic and biosynthetic needs.
This point is especially interesting because it connects the biology of the tumor cell with the tissues that surround it. The kidney tumor does not grow in isolation.
Among the factors associated with the development of renal carcinoma, obesity is especially relevant.
The research material indicates that an elevated body mass index is strongly associated with RCC and that obesity may increase the risk of developing the disease.
The proposed mechanisms include:
Hypertension also holds an important place among the factors associated with the rising incidence of renal carcinoma.
The obesity paradoxThere is also a particularly interesting phenomenon: although obesity increases the risk of developing RCC, several cohorts have observed that some obese patients with established disease, particularly metastatic disease, may have better survival than patients with a normal BMI. This phenomenon is known as the "obesity paradox".
Its mechanisms are still complex and probably include metabolic, immunological, and adipose tissue signaling differences.
The modern conception of cancer has moved beyond the idea of the tumor as a simple autonomous proliferation of malignant cells. Tumor cells interact continuously with their surroundings.
This tumor microenvironment is made up of multiple elements:
There is, therefore, a dynamic dialogue between the tumor and the surrounding tissues.
In renal carcinoma this concept is of particular interest because of the close anatomical relationship between the kidney and the perirenal adipose tissue.
Perirenal adipose tissue, known as PRAT (perirenal adipose tissue), lies between the renal capsule and Gerota's fascia.
It is one of the most abundant stromal components immediately surrounding the kidney and can establish a close relationship with the tumor, especially in locally advanced disease.
We now know that adipose tissue is not merely an energy store. It behaves as a true endocrine and immunological organ, capable of producing multiple biologically active substances, including:
This raises a particularly interesting question: can the adipose tissue surrounding the kidney modify the behavior of kidney cancer?
The experimental evidence presented in the thesis suggests that this interaction exists and that it is bidirectional.
Peritumoral adipose tissue does not appear to behave as a passive bystander.
The studies included in the research line presented in the thesis describe differences between peritumoral renal adipose tissue and normal renal adipose tissue. Conditioned media obtained from peritumoral adipose tissue produced, in experimental models, an increase in:
Differences were also observed in mediators such as leptin, versican, and perilipin, raising the possibility that adipose tissue takes an active part in regulating tumor behavior.
Another phenomenon under investigation is so-called browning, or "beiging," of adipose tissue.
In human samples of peritumoral tissue, changes were described from features typical of white adipose tissue toward a beige/brown phenotype, including morphological and molecular modifications. The markers studied include:
Functionally, this reprogramming can produce greater lipolysis and release of fatty acids, potentially generating energy substrates that tumor cells can use. Increased lactate production has also been observed, helping to metabolically modify the tumor microenvironment.
The interaction appears to be bidirectional:
Tumor → modifies adipose tissue → modified adipose tissue → may promote tumor behavior.
This model allows us to think of renal carcinoma as a true tumor ecosystem.
Angiogenesis is a central feature of clear cell renal carcinoma.
In addition to the VHL–HIF–VEGF pathway intrinsic to tumor cells, peritumoral adipose tissue may help create an environment favorable to the formation of new vessels.
The studies included in the thesis observed elevated VEGF levels in conditioned media from peritumoral adipose tissue, and an ability to promote endothelial cell migration and the formation of tubular structures in experimental models.
Changes consistent with epithelial-mesenchymal transition (EMT) were also described, a phenomenon related to the acquisition of migratory and invasive characteristics by tumor cells.
These findings remain an area of translational research and should not be interpreted as established clinical tools.
Molecular knowledge is not meant to turn the resident into a molecular biologist. Its purpose is to help them understand the disease they are treating.
When a urologist sees a hypervascular renal carcinoma, they should be able to relate it to its angiogenic biology.
When studying VEGF-targeted treatments, they should understand why this pathway is a therapeutic target.
When performing a partial nephrectomy and finding intensely adherent perirenal fat, they can recognize that this tissue is not necessarily a passive anatomical element.
From a surgical standpoint, so-called adherent perirenal fat can be anticipated with preoperative imaging. The Mayo Adhesive Probability Score (MAP Score) uses imaging features to estimate the probability of finding adherent fat and can help anticipate the difficulty of the dissection.
Integrating anatomy, imaging, surgery, and molecular biology is a more modern way of understanding renal carcinoma.
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