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Purpose Cabozantinib is an oral potent inhibitor of vascular endothelial growth factor receptor 2, MET, and AXL and is a standard second-line therapy for metastatic renal cell carcinoma (mRCC). This randomized phase II multicenter trial evaluated cabozantinib compared with sunitinib as first-line therapy in patients with mRCC.

Kidney cancer is a broad, encompassing term that borders on colloquial. While most physicians are referring to renal cell carcinoma when they say “kidney cancer”, a number of other benign and malignant lesions may similarly manifest as a renal mass. Considering only the malignant causes, kidney cancers may include renal cell carcinoma, urothelium-based cancers (including urothelial carcinoma, squamous cell carcinoma, and adenocarcinoma), sarcomas, Wilms tumor, primitive neuroectodermal tumors, carcinoid tumors, hematologic cancers (including lymphoma and leukemia), and secondary cancers (i.e. metastases from other solid organ cancers).

Epidemiology

In the United States, cancers of the kidney and renal pelvis comprise the 6th most common newly diagnosed tumors in men and 10th most common in women.¹ In 2018, an estimated 65,340 people will be newly diagnosed with cancers of the kidney and renal pelvis in the United States. In men, this comprises 42,680 estimated new cases in 2018 representing 5% of all newly diagnosed cancers. In women, 22,660 new cases are anticipated in 2018 representing 3% of all newly diagnosed cancers. Additionally, 14,970 people are expected to die of kidney and renal pelvis cancers in 2018 in the United States, with this being the 10^th most common cause of oncologic death among men.

In Europe, results are similar. In 2018, the incidence of kidney cancer is estimated at 136,500 new cases representing 3.5% of all new cancer diagnoses.² This corresponds to an estimated age standardized rate (ASR) of 13.3 cases per 100,000 population. As in the United States, the incidence of kidney and renal pelvis cancers is higher among men (incidence 84,9000, 4.1% of all cancers, ASR 18.6 per 100,000) than women (incidence 51,600, 2.8% of all cancers, ASR 9.0 per 100,000). Correspondingly, 54,700 people were estimated to die of kidney and renal pelvis cancers in Europe in 2018, accounting for 2.8% of all oncologic deaths. The age standardized mortality rate was 4.7 deaths per 100,000 population. Again, death from kidney and renal pelvis cancer was more common among men (mortality 35,100, 3.3% of oncologic deaths, ASR 7.1 per 100,000) than among women (mortality 19,600, 2.3% of oncologic deaths, ASR 2.7 per 100,000). Interestingly, within Europe, there is considerable variation in the incidence and mortality of kidney and renal pelvis cancer between countries.²

While the aforementioned data have already demonstrated that gender is strongly associated with the risk of both diagnosis of and death from kidney and renal pelvis cancers, age also importantly moderates this risk. Among patients in the United States, the probability of developing kidney and renal pelvis cancer rises nearly ten fold from age <50 to age >70 years.¹

Thus, kidney cancer is predominantly a disease of older adults, with the typical presentation being between 50 and 70 years of age. However, over time, rates of diagnosis of kidney cancer have increased fastest among patients aged less than 40 years old.³

In the United States, kidney cancers are more common among African Americans, American Indians, and Alaska Native populations while rates are lower among Asian Americans.⁴ Worldwide, the highest rates are found in European nations while low rates are seen in African and Asian countries.⁴

The vast majority of patients have localized disease at the time of presentation. According to Siegel et al., 65% of all patients diagnosed with kidney and renal pelvis tumors between 2007 and 2013 had localized disease at the time of presentation while 16% had regional spread and 16% had evidence of distant, metastatic disease.¹ This is in large part due to incidental diagnosis due to the increased use of ultrasonography and computed tomography in patients presenting with abdominal distress. In fact, 13 to 27% of abdominal imaging studies demonstrate incidental renal lesions unrelated to the reason for the study⁵ and approximately 80% of these masses are malignant.⁶ Dr. Welch and colleagues demonstrated elegantly that the use of computed tomography is strongly related to the likelihood of undergoing nephrectomy, likely due to detection of renal masses. Thus, with the increasing utilization of abdominal imaging, the incidence of kidney cancer has increased by approximately 3 to 4% per year since the 1970s.

Renal Cell Carcinoma

Renal cell carcinoma (RCC) is the most common kidney cancer. A number of histological subtypes have been recognized including conventional clear cell RCC (ccRCC), papillary RCC, chromophobe RCC, collecting duct carcinoma, renal medullary carcinoma, unclassified RCC, RCC associated with Xp11.2 translocations/TFE3 gene fusions, post-neuroblastoma RCC, and mucinous tubular and spindle cell carcinoma. Conventional ccRCC comprises approximately 70-80% of all RCCs while papillary RCC comprises 10-15%, chromophobe 3-5%, collecting duct carcinoma <1%, unclassified RCC 1-3%, and the remainder are very uncommon.

Histologically, most of these tumors are believed to arise from the cells of the proximal convoluted tubule given their ultrastructural similarities. Renal medullary carcinoma and collecting duct carcinoma, relatively uncommon and aggressive subtypes of RCC, are believed to arise more distally in the nephron.

Familial RCC Syndromes

While the vast majority of newly diagnosed RCCs are sporadic, hereditary RCCs account for approximately 4% of all RCCs. Due in large part to the work of Dr. Linehan and others, the understanding of the underlying molecular genetics of RCC have progressed significantly since the early 1990s. These insights have led to a better understanding of both familial and sporadic RCCs.

Von Hippel-Lindau disease is the most common cause of hereditary RCC. Due to defects in the VHL tumor suppressor gene (located at 3p25-26), this syndrome is characterized by multiple, bilateral clear cell RCCs, retinal angiomas, central nervous system hemangioblastomas, pheochromocytomas, renal and pancreatic cysts, inner ear tumors, and cystadenomas of the epididymis. RCC develops in approximately 50% of individuals with VHL disease. These tumors are characterized by an early age at the time of diagnosis, bilaterality, and multifocality. Due in large part to improved management of the CNS disorders in VHL disease, RCC is the most common cause of death in patients with VHL.

Hereditary papillary RCC (HPRCC) is, as one would expect from the name, associated with multiple, bilateral papillary RCCs. Due to an underlying constitutive activation of the c-Met proto-oncogene (located at 7q31), these tumors also present at a relatively early age. However, overall, these tumors appear in general to be less aggressive than corresponding sporadic malignancies.

In contrast, tumors arising in hereditary/familial leiomyomatosis and RCC (HLRCC), due to a defect in the fumarate hydratase (1q42-43) tumor suppressor gene, are typically unilateral, solitary, and aggressive. Histologically, these are typically type 2 papillary RCC, which has a more aggressive phenotype, or collecting duct carcinomas. Extra-renal manifestations include leiomyomas of the skin and uterus and uterine leiomyosarcomas which contribute to the name of this sydrome.

Birt-Hogg-Dube, due to defect in the tumor suppressor folliculin (17p11), is associated with multiple chromophobe RCCs, hybrid oncocytic tumors (with characteristics of both chromophobe RCC and oncocytoma), oncocytoma. Less commonly, patients with Birt-Hogg-Dube may develop clear cell RCC or papillary RCC. Non-renal manifestations include facial fibrofolliculomas, lung cysts, and the development of spontaneous pneumothorax.

Tuberous sclerosis, due to defects in TSC1 (located at 9q34) or TSC2 (16p13), may lead to clear cell RCC. More commonly, it is associated with multiple benign renal angiomyolipomas, renal cystic disease, cutaneous angiofibromas, and pulmonary lymphangiomyomatosis.

Succinate dehydrogenase RCC, due to defects in the SDHB (1p36.1-35) or SDHD (11q23) subunits of the succinate dyhydrogenase complex, may lead to a variety of RCC subtypes including chromophobe RCC, clear cell RCC, and type 2 papillary RCC. Extra-renal manifestations including benign and malignant paragangliomas and papillary thyroid carcinoma. In general, these tumors exhibit aggressive behaviour and wide surgical excision is recommended.

Finally, Cowden syndrome, due to defects in PTEN (10q23) may lead to papillary or other RCCs in addition to benign and malignant breast tumors and epithelial thyroid cancers.

Etiologic Risk Factors in Sporadic RCC

While numerous hereditary RCC syndromes exist, they account for only 4% of all RCCs. However, many sporadic RCCs share similar underlying genetic changes including VHL defects in ccRCC and c-Met activation in papillary RCC. A number of modifiable risk factors associated with RCC have been described.⁴

The foremost risk factor for the development of RCC is cigarette smoking. According to both the US Surgeon General and the International Agency for Research on Cancer, observational evidence is sufficient to conclude there is a causal relationship between tobacco smoking and RCC. A comprehensive meta-analysis of western populations demonstrated an overall relative risk for the development of RCC of 1.38 (95% confidence interval 1.27 to 1.50) for ever smokers compared to lifetime never smokers.⁷ Interestingly, this effect was larger for men (RR 1.54, 95% CI 1.42-1.68) than for women (RR 1.22, 95% CI 1.09-1.36). Additionally, there was a strong dose response relationship: compared to never smokers, men who smoked 1-9 cigarettes per day had a 1.6x risk, those who smoked 10-20 per days had a 1.83x risk, and those who smoked more than 21 per day had a 2.03x risk. A similar trend was seen among women. Notably, the risk of RCC declined with increasing durations of abstinence of smoking. Smoking appears to be preferentially associated with the development of clear cell and papillary RCC.⁸ In addition to being associated with increased RCC incidence, smoking is associated with more aggressive forms of RCC, manifest with higher pathological stage and an increased propensity for lymph node involvement and metastasis at presentation.⁹ As a result, smokers have worse cancer-specific and overall survival.⁹

Second, obesity is associated with an increased risk of RCC. While this risk was historically felt to be higher among women, a more recent review demonstrated no such effect modification according to sex.¹⁰ In a meta-analysis of 22 studies, Bergstrom et al. estimated that each unit increase of BMI was associated with a 7% increase in the relative risk of RCC diagnosis.

Third, hypertension has been associated with an increased risk of RCC diagnosis, with a hazard ratio of 1.70 (95%CI 1.30-2.22) in the VITAL study.¹¹ Interestingly, in an American multiethnic cohort, this effect appeared to be larger among women (RR 1.58, 95% CI 1.09-2.28) than in men (RR 1.42, 95% CI 1.07-1.87).¹² Again, as with obesity, there appears to be a dose-effect relationship between severity of hypertension and the risk of RCC diagnosis.¹³

Fourth, acquired cystic kidney disease (ACKD) appears to be associated with a nearly 50x increase risk of RCC diagnosis.¹⁴ ACKD occurs in patients with end-stage renal disease on dialysis. These changes are common among patients who have been on dialysis for at least 3 years.¹⁴ Interestingly, the risk of RCC appears to decrease following renal transplantation.

Finally, a number of other putative risk factors have been described. These lack the voracity of data that the aforementioned four have. Such risk factors include alcohol, analgesics, diabetes, and diet habits.⁴

Background

Risk Stratification

Favorable Risk Patients

Intermediate and Poor Risk

Future Therapies

Cytokine Therapies for Advanced ccRCC

Inhibitors of the VEGF Pathway for Advanced ccRCC

Inhibitors of mTOR for Advanced ccRCC

Checkpoint Inhibitors for Advanced ccRCC

Other Agents for Advanced ccRCC

Treatment of Advanced non-ccRCC

Integration of treatment options for patients with advanced RCC

Background 

Kidney cancer is the 12^th most common cancer in the world, with over 300,000 new cases annually, of which 65,340 new cases will be diagnosed in the United States in 2018.¹ The incidence of renal cell carcinoma (RCC) varies substantially based on the country – rates of RCC are higher in Europe and North America and much lower in Asia and South America.²

Most kidney cancers (>90%) are renal cell carcinomas, and of renal cell carcinomas, the majority of cases (80%) will be the clear cell subtype.³ Of the remaining 20% of cases, the two major histological subtypes are papillary (10-14%) and chromophobe (5%)^3,4, but also include collecting duct, translocation carcinoma, medullary carcinoma, and unclassified RCC. These histological subtypes are distinct from clear cell carcinoma and independently predict for survival.³ For example, after controlling for TNM status, age, gender, and tumor size, patients with early stage clear cell RCC are more than twice as likely to die of RCC than patients with papillary or chromophobe RCC.³ Some of these subtypes also have unique risk factors. For example, renal medullary carcinomas are an aggressive non-clear cell carcinoma that are almost exclusively associated with patients with sickle cell trait.⁵

Non-clear cell RCCs (ncRCC) also have unique mutational landscapes.⁶ For example, MET mutations can be found in 15-30% of papillary RCCs.^6,7 Papillary RCCs also have a higher mutation rate compared with chromophobe RCCs and renal oncocytomas. Durinck et al evaluated 167 primary human tumors including papillary, chromophobe and translocation subtypes and were able to use a five gene set to help molecularly distinguish between chromophobe carcinoma, renal oncocytoma and papillary carcinoma.⁶

Treatment

Given the rarity of non-clear cell RCC (ncRCC), there is a paucity of large randomized phase III trials to help guide the optimal therapy for ncRCC. Some trials for ncRCC have had to stop due to slow accrual. Given this lack of data, patients are encouraged to participate in clinical trials when they are available and appropriate. Below is a summary of the most common systemic therapies in use for ncRCC.

Sunitinib

Single agent sunitinib has been evaluated as part of an expanded access trial as well as several small phase II trials (Table 1). In a single arm phase II clinical trial, 23 patients were given sunitinib 50 mg in cycles of four weeks on followed by 2 weeks off. The trial was stopped early due to slow accrual and the median progression free survival (PFS) was 5.5 months.⁸  In a another phase II trial evaluating both sunitinib and sorafenib, 19 patients with ncRCC were given sunitinib – median PFS was 11.9 months in the papillary arm and 8.9 months in the chromophobe arm.⁹ The largest of these studies was reported by Gore et al, which included 588 ncRCC patients who received sunitinib as part of the expanded access study encompassing 4564 RCC patients who received sunitinib.¹⁰ In their study, 11% of patients had an objective response and median PFS was 7.8 months. Some trials have stratified outcomes by histological subtypes such as chromophobe or papillary, and one trial reported results broken down by type 1 papillary RCC vs type 2 papillary RCC11. Overall, most studies demonstrated that sunitinib led to a median PFS of about 6-7 months for ncRCC.

Everolimus and Temsirolimus

mTOR inhibitors Everolimus and Temsirolimus have been evaluated by a few phase II trials for ncRCC (Table 2). Everolimus was evaluated in a subgroup of REACT (RAD001 Expanded Access Clinical Trial in RCC) and in RAPTOR (RAD001 in Advanced Papillary Tumor Program in Europe).^15,16 In REACT, 1.3% of patients with ncRCC had a partial response and 49.3% had stable disease.¹⁵ In RAPTOR, the median progression free survival (mPFS) was 4.1 months and median OS was 21.4 months. For patients with chromophobe RCC, mTOR directed therapy may be especially effective – case reports show partial responses and stable disease to both Everolimus or Temsirolimus.^17,18 This may be due to the hypothesis that a high number of chromophobe RCC’s have PI3K-mTOR pathway activation as well as frequent TSC1/TSC2 mutations which may sensitize these tumors to mTOR inhibition.¹⁹ 

Sunitinib vs Everolimus

Sunitinib and everolimus have also been examined head to head. The largest trial was ASPEN (Everolimus versus sunitinib for patients with metastatic non-clear-cell renal cell carcinoma), a multicenter open-label, randomized phase II trial which randomized 108 patients to receive either sunitinib or everolimus.²² The primary endpoint of this study was progression free survival. The majority of patients had papillary histology (65%). Median overall survival was 13.2 months in the everolimus group and 31.5 months in the sunitinib group. However, overall survival was not statistically different between the two treatment groups (HR 1.12, 95%CI 0.7-2.1, p=0.6). A second study, ESPN (Everolimus Versus Sunitinib Prospective Evaluation in Metastatic Non–Clear Cell Renal Cell Carcinoma) came to a similar conclusion and found that the median overall survival was 16.2 months with sunitinib and 14.9 months with everolimus (p=0.18).²³

While overall survival between everolimus and sunitinib were not statistically different for the unselected cohorts, ASPEN did find differences in objective responses between the different subtypes, suggesting that each subtype of ncRCC may respond differently to therapies. In ASPEN, 24% (8/33) of papillary RCCs achieved a partial or complete radiographic response on sunitinib compared with 5% of patients on everolimus (2/37). Interestingly, clinical outcomes after receipt of either sunitinib or everolimus also varied based on risk stratification. Patients with good or intermediate risk had improved median progression free survival (mPFS) with first line sunitinib than everolimus. However, patients with poor risk had improved PFS with everolimus over sunitinib. This is concurrent with the ARCC trial, which also demonstrated improved overall survival with an mTOR inhibitor (temsirolimus) in poor risk patients with ncRCC.²⁴

A meta-analysis of five studies (ESPN, ASPEN, RECORD3, ARCC, and SWOG1107) found a nonstatistical trend favoring sunitinib over everolimus for ncRCC but does note that there is considerable patient heterogeneity in these small studies and there was no statistical difference in PFS between these two therapies.²⁵ In the absence of clinical trial options, sunitinib is a reasonable first line choice for treatment naïve patients with ncRCC, especially for those with papillary RCC or MSKCC good risk RCC.

Special Populations

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Future Direction

A number of active clinical trials are in progress, investigating various MET inhibitors as well as checkpoint inhibitors for ncRCC (Table 3). Preliminary data suggest that PD-1 or PD-L1 blockade may have some activity in this population.^30,31 Given the dearth of data and rarity of ncRCC, it is important to consider these patients for clinical trials, whenever possible.