BERKELEY, CA (UroToday.com) - Renal cancer is currently the thirteenth most common malignancy in the world with an incidence that continues to increase.
The main reason for the increasing incidence of renal cancer diagnosis is by far the abundant use of imaging, mainly for unrelated reasons. It is estimated that almost 70% of renal masses are organ-confined at diagnosis and a significant portion of them, mainly those smaller than 3 cm, may also carry a benign prognosis.
Still, although there is significant evolution in the diagnosis and detection of renal tumors, little improvement has been shown with regard to the survival of patients with advanced and metastatic disease. At present it is estimated that about 20-30% of patients have metastatic disease at diagnosis while another 20% will present with distant recurrence after radical nephrectomy. Given the dismal prognosis of metastatic renal cancer, reducing the risk of metastases is crucial for improving quality of life and overall survival for these patients.
Towards this end, there have been efforts to improve local staging and prognosis by the implementation of a variety of tumor markers and sophisticated imaging studies, however with limited clinical efficacy. Another factor that may account for the significant risk of metastases from renal cancer is the unpredictable pattern of lymphatic drainage of renal tumors. The impact of lymph node status on prognosis and survival for patients with renal tumors cannot be overemphasized. Therefore, and given the inability of imaging studies to accurately define the lymph node status due to false-negative results, lymph node dissection may be key in providing knowledge of the real status of lymph nodes, thereby improving staging accuracy and consequently effecting the patient’s ultimate prognosis.
However the absence of an accepted standardized approach to retroperitoneal lymph node dissection contributes to the uncertainty about the benefits of lymph node dissection for renal tumors. In addition, recent evidence of the complex and unpredictable pattern of lymph node drainage of the kidney further contributes to the lack of consensus over the template for lymph node dissection. The practice patterns of urologists in the United States, as demonstrated in a recent survey, verify the lack of consensus on the role or even the definition of lymph node dissection for renal tumors. At the time of radical nephrectomy for a localized renal tumor, 26% of practicing urologists do not perform a formal lymph node dissection, whereas 41% perform a limited node dissection and 33% perform a full retroperitoneal lymph node dissection extending from the crus of the diaphragm to the bifurcation of the aorta or vena cava.
All these factors may be held responsible for the increased incidence and the rare sites of distal metastases that are detected even years following radical nephrectomy. The present review has focused in assessing the variability of metastases that arise in areas and organs that are anatomically distant to the kidney and outside of what would be considered the “usual pathway” of metastatic spread.
The landing sites of distant metastases from renal cancer have been fascinating. For instance it is interesting to know that renal cancer is the third most frequent neoplasm to metastasize to the head and neck region preceded only by breast and lung cancer, and that the tongue is a frequent site for metastases from renal cancer. Moreover, metastases from renal cancer have been detected to the orbit, parotid gland, nasal and paranasal cavities and skin in up to 3% of cases. Tumor involvement of the paranasal sinuses and nasal fossae appears to occur via the hematogenous route through the Batson’s paravertebral venous plexus which is also considered the culprit for bone metastases from prostate cancer. This anastomotic network of avalvular veins surrounding the bone marrow and vertebras is connected with pelvic, intercostal, azygos and cava veins and allows for tumor seeding in both a caudal direction toward the pelvis and in a cranial direction. Increased intra-abdominal or intrathoracic pressure causes an increased flow to the paravertebral plexus, from which venous sinuses in the calotte, and retrogradely the pterygoid plexus, are reached before arriving at the paranasal sinuses. This explains how tumor cells may escape the pulmonary capillary filter and how renal and other genitourinary tumors can metastasize into the paranasal sinuses.
Given that the prognosis for patients with distant metastases from renal cancer in universally poor with only palliative symptomatic treatment available, one can conclude that despite recent advancements in diagnosis, imaging, and local control of the disease, renal cancer continues to represent a potentially lethal cancer that is associated with aggressive behavior and has a high propensity for metastatic spread.
Petros Sountoulides, MD, PhD, FEBU and Luca Cindolo, MD, FEBU as part of Beyond the Abstract on UroToday.com. This initiative offers a method of publishing for the professional urology community. Authors are given an opportunity to expand on the circumstances, limitations etc... of their research by referencing the published abstract.