Renal cancer. Contemporary management. Editor John A. Libertino. Springer New York 2013.
Due to the increased utilization of cross-sectional abdominal imaging, we have witnessed a signiﬁcant stage migration with the incidental detection of small clinically localized renal masses <4 cm. The gold standard for the management of enhancing renal lesions remains surgical excision. Cancer-speciﬁc mortality remains unchanged despite a concurrent increase in surgical resection rates. This implies that a proportion of these SRMs may be indolent tumors that may not require curative intervention. Despite the limited contemporary body of literature on the natural history of untreated SRMs, recent pooled data demonstrate that the vast majority demonstrate slow growth kinetics with a very low rate of progression to metastatic disease. A signiﬁcant percentage (20–30%) of SRMs exhibit zero net growth under observation. It appears that malignancy rates are equivalent in zero growth lesions when compared to lesions demonstrating positive growth; however, to date, no zero growth lesion has progressed to metastatic disease nor has any SRMs <3 cm at the time of progression. Lesions that are more likely to progress to metastases under observation tend to be larger at diagnosis with a high nuclear grade and signiﬁcantly more rapid growth kinetics. In addition, metastatic progression in these patients appears to be a late event. Despite these observations, improved methods of recognizing lesions with more aggressive biologic potential at the time of presentation are needed. Until such metrics are available, our clinical decision making will be dependent on tumor linear growth rate. For SRMs that demonstrate rapid growth kinetics, one should strongly consider immediate deﬁnitive intervention. Lesions exhibiting zero or minimal growth appear to be safe for continued AS. As the experience with AS progress, we anticipate that improved imaging techniques, utilization of percutaneous biopsy, and biomarker discovery will allow physicians to more conﬁdently match treatment to individual tumor biology. Until then, use of preoperative nomograms to stratify SRMs malignant potential and account for competing medical risks will remain valuable in treatment planning. Ideally randomized prospective trials would be performed to evaluate the efﬁcacy of AS. In the absence of level I data, AS for localized solid renal masses remains an alternative treatment strategy to deﬁnitive extirpation in select patients with limited life expectancy, competing comorbidities that preclude operative intervention, or signiﬁcant risk of requiring hemodialysis following intervention. When discussing observation of the incidentally diagnosed SRMs, patients and clinicians must calculate and accept the risks of surveillance. These risks must be weighed against the risk of intervention when considering all treatment trade-off decisions.