Evolving understanding and surgical management of renal cortical tumors

Renal cortical tumors: use of multiphasic contrast-enhanced MR imaging to differentiate benign and malignant histologic subtypes

PURPOSE

To investigate the use of quantitative multiphasic contrast material-enhanced magnetic resonance (MR) imaging in differentiating between common benign and malignant histologic subtypes of renal cortical tumors.

MATERIALS AND METHODS

The institutional review board waived informed consent and approved this retrospective HIPAA-compliant study of 138 patients who underwent preoperative contrast-enhanced MR imaging during the period of January 2004-December 2008. At surgery, 152 renal tumors were identified (77 clear cell, 22 papillary, 18 chromophobe, and 10 unclassified carcinomas; 16 oncocytomas; nine angiomyolipomas). Three readers independently identified and measured the most-enhanced area in each tumor and placed corresponding regions of interest in similar positions on images from the precontrast, corticomedullary, nephrographic, and excretory phases. The percentage change in signal intensity (%SI change) between precontrast imaging and each postcontrast phase was calculated. Interreader agreement was evaluated by using the overall concordance correlation coefficient (OCC). A linear mixed-effects model was used to estimate and compare the trajectories of the means of log %SI change across all phases between the six histologic subtypes.

RESULTS

Interreader agreement was substantial to almost perfect (OCC, 0.77-0.88). The %SI change differed significantly between clear cell carcinomas and papillary and chromophobe carcinomas in all phases of enhancement (P < .0001-.0120). In addition, %SI change was significantly higher in angiomyolipomas than in clear cell carcinomas, but only in the corticomedullary phase (P = .0231). Enhancement did not differ significantly between clear cell carcinoma and oncocytoma in any phase (P = .2081-.6000).

CONCLUSION

Quantitative multiphase contrast-enhanced MR imaging offers a widely available, reproducible method to characterize several histologic subtypes of renal cortical tumors, although it does not aid differentiation between clear cell carcinomas and oncocytomas.

Distribution of renal tumor growth rates determined by using serial volumetric CT measurements

PURPOSE

To retrospectively determine the distribution of growth rates across different sizes and subtypes of renal cortical tumors by assessing tumor volume and maximum tumor diameter at serial volumetric computed tomographic (CT) examinations.

MATERIALS AND METHODS

The institutional review board approved this retrospective, HIPAA-compliant study. Fifty-three of 2304 patients (34 men, 19 women; mean age, 67 years +/- 10 [standard deviation; range, 39-88 years) who underwent nephrectomy from 1989 to 2006 did not receive preoperative chemotherapy or radiation therapy and underwent at least two preoperative contrast material-enhanced CT examinations (at least 3 months apart) with identical section thickness that was no more than one-fifth of longitudinal tumor diameter. Tumor volume and maximum diameter were measured on CT scans. Reciprocal of doubling time (DT) (RDT) was calculated. Analysis of variance and Student t tests were performed.

RESULTS

Thirty-two clear cell carcinomas, 10 papillary carcinomas, six chromophobe carcinomas, four oncocytomas, and one angiomyolipoma were analyzed. Median tumor size was 2.9 cm (range, 1-12 cm). Seven tumors did not increase in volume. DT ranged from -78476.54 to 18057.43 days (mean, -1230.73 days; median, 590.51 days). [corrected] Growth rate determined by using maximum diameter ranged from -10.8 to 33.2 mm/y (mean, 5.1 mm/y; median, 3.5 mm/y). Faster-growing tumors were more likely to be clear cell carcinomas, those of higher grade had higher growth rates. No significant correlation was found between RDT and tumor initial volume, subtype, or grade. Small renal tumors (<or=3.5 cm) were similar to larger tumors in subtype and growth rate. Age at diagnosis correlated negatively with renal tumor growth rate (P = .03).

CONCLUSION

Growth rates in renal tumors of different sizes, subtypes, and grades represent a wide range and overlap substantially. Small renal tumors appear to be similar to larger ones in nature.

[Sporadic kidney cancer in patients younger than 45]

INTRODUCTION

The incidence of kidney cancer is constantly increasing. The objective of this study was to report the characteristics of sporadic kidney tumours observed in a population of patients under the age of 45 years and to define prognostic factors based on a 5-year follow-up.

MATERIAL AND METHODS

Between 1985 and 2003, 64 patients, with a mean age of 38 +/- 7 years, presenting with sporadic kidney cancer were included in this retrospective study.

RESULTS

Sporadic kidney cancer was discovered incidentally in 39.1% of young adults, predominantly in women. Radical nephrectomy was performed in 57 cases and partial nephrectomy was performed in 5 cases. The distribution by histological type was comparable to that of the general population, but pathological examination of carcinomas showed a high Führman grade in 66% of cases. The mean follow-up was 72 59 months. The 3-year and 5-year overall survival was 79% and 76.7% respectively. The mortality rate was 25%: 13 specific deaths and 3 nonspecific deaths. TNM stage was a prognostic factor on univariate and multivariate analysis. The mode of discovery and the ASA score were also identified as prognostic factors on univariate analysis.

CONCLUSION

Sporadic kidney cancer is rare in adults before the age of 45 years and presents with symptoms. Earlier detection would allow an improvement of the prognosis.

A novel murine model for the study of human renal cryoablation

OBJECTIVE

to develop a reproducible, non-debilitating in vivo murine model of human renal cryoablation using a standard closed argon-delivery system.

MATERIALS AND METHODS

Custom engineered 2-mm conical tip cryoprobes for use on the standard argon-based cryoablation unit (Endocare, Inc. Irvine, CA, USA) were used to create small controllable iceballs (−160 °C) in the mouse kidney. The time to create a 4-mm cryolesion was compared using a contact vs puncture technique in 10 mice. To show consistency of the induced-freeze injury, a 4-mm iceball was created in 20 murine renal units and the time to creation and the size of the resultant cryolesion measured. To investigate lesion regression and histological changes, we created a 4-mm renal cryolesion in 28 mice and killed four each at 1, 3, 7, 14, 21, 28, and 35 days. The measured coronal cross-sectional area of the cryoablation site at necroscopy was compared to the initial calculated area as a percentage. To assess renal preservation, blood urea nitrogen (BUN) and creatinine levels at 1 week after cryoablation or sham ablation was compared (10 mononephric mice in each group).

RESULTS

The time to create the desired iceball was 1.9 times quicker using the puncture vs the contact technique. The mean (sd) time to forming a 4-mm iceball was 35.3 (4.8) s with a mean maximum length of the resultant post-thaw injury of 5.7 (0.5) mm and a 9% coefficient of variance. Regression analysis of the two-dimensional cross-sectional coronal area of the cryolesion showed a statistically significant linear pattern of regression over time (P = 0.037) and classic histological findings. There was no significant difference in the BUN or creatinine levels in mononephric mice 1 week after cryotherapy compared with the sham-ablated controls.

CONCLUSIONS

We describe a reproducible, non-debilitating, easily manipulated murine model for the study of human renal cryoablation.

Efficacy and Safety of TachoSil ® as Haemostatic Treatment versus Standard Suturing in Kidney Tumour Resection: A Randomised Prospective Study

OBJECTIVE

Elective nephron-sparing surgery (NSS) for renal cell carcinoma (RCC) has gained general acceptance as an alternative to radical nephrectomy. To achieve haemostasis without risk of local ischaemia and necrosis of kidney parenchyma after standard haemostatic suturing, we investigated TachoSil's efficacy and safety as atraumatic haemostatic treatment after kidney tumour resection.

METHODS

A total of 185 patients scheduled for NSS for small, superficial kidney tumours were included in an open, randomised, prospective, multicentre, parallel-group trial. Primary objectives were to test haemostatic efficacy and safety of TachoSil versus standard suturing. Efficacy was tested by comparing intraoperative time to haemostasis (primary end point). Secondary objectives included proportion of subjects with haemostasis after 10 min of trial treatment, occurrence of haematoma on day 2 after surgery, volume and haemoglobin concentration of postoperative drainage fluid, and surgeon's rating of usefulness of trial treatments. Safety was evaluated by occurrence of adverse events.

RESULTS

In the intent-to-treat population, time to haemostasis was significantly shorter with TachoSil versus standard suturing (mean: 5.3 vs. 9.5 min [p<0.0001]). Haemostasis was obtained within 10 min in 92% of patients in the TachoSil group and in 67% in the standard treatment group (p<0.0001). Differences in other secondary end points were not statistically significant. Both treatments were well tolerated. Surgeons rated TachoSil higher in terms of convenience to prepare and apply, and impression of efficacy.

CONCLUSION

TachoSil was superior to standard suturing in obtaining intraoperative control of haemorrhage and was as well tolerated as standard haemostatic treatment during NSS.

Solid renal cortical tumors: differentiation with CT

PURPOSE

To retrospectively determine if solid renal cortical tumors can be differentiated on computed tomographic (CT) images on the basis of their morphologic features and enhancement patterns.

MATERIALS AND METHODS

Institutional review board approval was obtained and the informed consent requirement was waived for this HIPAA-compliant study. Between January 2004 and September 2005, 193 consecutive patients (age range, 19-95 years; 112 men, 81 women) with renal masses underwent total or partial nephrectomy and preoperative renal CT. Two radiologists retrospectively reviewed CT studies in an independent and blinded fashion. The pattern and degree of enhancement, lesion contour, presence of neovascularity, and calcifications were evaluated. Fisher exact tests, Pearson chi(2) tests, multivariate logistic regression, and Wilcoxon rank sum tests were performed.

RESULTS

Of the 198 renal tumors (median size, 3.4 cm; range, 1.1-20.0 cm) included in this study, 108 (55%) were clear cell renal cell carcinomas (RCCs); 30 (15%), papillary lesions; 24 (12%), chromophobe adenomas; 14 (7%), oncocytomas; six (3%), lipid-poor angiomyolipomas; and 16 (8%), other or unclassified renal tumors. Clear cell RCC most commonly manifested with a mixed enhancement pattern of both hypervascular soft-tissue components and low-attenuation areas that corresponded to necrotic or cystic changes (reader 1, 88% of clear cell tumors; reader 2, 79% of clear cell tumors). This pattern was highly predictive of clear cell RCC (odds ratio of 22 and 54 for readers 1 and 2, respectively, for comparison with homogeneous pattern), whereas the homogeneous and peripheral enhancing patterns were more predictive of less aggressive papillary and chromophobe lesions. Clear cell RCCs and oncocytomas tended to be hypervascular, chromophobe lesions and angiomyolipomas tended to enhance moderately, and papillary lesions were mostly hypovascular.

CONCLUSION

Certain imaging features and the degree of enhancement may be helpful in differentiating subtypes of renal cortical tumors.

Significance of Peritumoral Vascularity on CT in Evaluation of Renal Cortical Tumor

PURPOSE

To investigate whether the presence and degree of peritumoral vascularity may provide any diagnostic information regarding the histological subtypes of renal tumors.

MATERIALS AND METHODS

Between January 2004 and March 2006, 214 patients (age, 19-94 years; 120 men, 94 women) with renal masses underwent total or partial nephrectomy and preoperative renal protocol computed tomography. Two radiologists retrospectively reviewed the computed tomographic exams in an independent and blinded fashion. The radiologists evaluated the presence of peritumoral vascularity and measured the largest vessel caliber. Fisher exact tests, multivariate logistic regression, and Wilcoxon rank-sum tests were performed for statistical analysis.

RESULTS

Of 219 renal tumors (median size, 3.5 cm; range, 0.9-20.0 cm) included in this study, 112 (51%) were clear cell renal cell carcinoma, 34 (16%) were papillary, 32 (15%) were chromophobe, 17 (8%) were oncocytomas, 6 (3%) were lipid-poor angiomyolipomas, and 18 (8%) were other or unclassified renal tumors. The presence of peritumoral vascularity was significantly associated with tumor size within each subtype. For both readers, peritumoral vascularity was more frequently identified in clear cell carcinomas than in papillary renal carcinomas of similar size (P = 0.019 and 0.008, respectively). For one of the readers, chromophobe carcinomas were also significantly less frequently associated with peritumoral vascularity than clear cell carcinomas of similar size (P = 0.014).

CONCLUSIONS

Clear cell carcinomas demonstrate peritumoral vascularity significantly more frequently than other malignant renal tumors of similar size. The presence of peritumoral vascularity may provide additional diagnostic information and improve therapeutic planning in some cases.

Imaging of kidney cancer

Advances in molecular genetics have expanded the understanding of renal cell tumors. Now it is understood that renal cortical tumors are a family of neoplasms with distinct cytogenetics and molecular defects, unique histopathologic features, and different malignant potentials. Imaging contributes to clinical management of patients with renal tumors in providing diagnostic information for tumor detection, characterization, staging, treatment planning, and follow-up.

The impact of tumour location on the histological subtype of renal cortical tumours

OBJECTIVE

To determine whether the location of renal cortical tumours (RCTs) is a possible factor affecting tumour behaviour, by investigating whether exophytic vs a central location is associated with a difference in histological subtype distribution, as recognized prognostic factors for RCTs include size, stage, grade, and histological subtype.

PATIENTS AND METHODS

Between 1 January 1996 and 1 June 2003, we evaluated 485 consecutive RCTs in 469 patients who had renal imaging studies and underwent either partial or radical nephrectomy at our institution. A radiologist and a urologist independently reviewed the imaging studies of all patients to determine exophytic vs central location. An exophytic lesion was defined as one that clearly both pushed out the renal contour and did not extend into the collecting system, hilum, or renal sinus. A lesion that did not meet these criteria was defined as a central lesion. Logistic regression analysis was used to determine if either type of lesion had a greater representation of any histological subtype. A two-tailed P < or = 0.05 was considered to indicate significance.

RESULTS

Of the 485 RCTs, 171 (35%) were exophytic and 314 (65%) were central, while 308 (64%) were clear cell and 177 (36%) were non-clear cell tumour histology. Of the exophytic lesions, 52.0% were clear cell, while 69.7% of central lesions were clear cell (P < 0.001). Conversely, 71.1% of clear cell tumours were central, while 53.7% of non-clear cell tumours were central (P = 0.003). After controlling for size and stage, tumour location remained associated with histological subtype (P = 0.003).

CONCLUSIONS

Exophytic lesions are significantly more likely than central lesions to be non-clear cell tumours, and clear cell tumours are significantly more likely than non-clear cell tumours to be central. As studies indicate that the clear cell histological subtype portends a worse prognosis than the non-clear cell subtype, our results imply that tumour location affects the prognosis in RCTs, with exophytic lesions having a better prognosis than central lesions. This result may have important implications for physicians and patients when planning partial vs radical nephrectomy by either open or minimally invasive techniques.

Evaluation of imaging-guided fine-needle percutaneous biopsy of renal masses

To evaluate the utility of imaging-guided fine-needle percutaneous biopsy of renal masses, we conducted a prospective analysis of our imaging-guided procedures from January 1999 to February 2003. We performed 54 percutaneous core biopsies in 46 patients. Fluoro-computed tomography and ultrasound guidance were respectively used in 48 and six cases. One to four specimens were obtained by using an 18-gauge automated coaxial biopsy system. We reviewed the patients medical records, pathology results, and imaging studies. Core biopsy results were compared with surgical pathology (n=27) or clinical follow-up (n=19). All biopsies provided sufficient material for analysis. The mean tumor size was 33 mm. Biopsy findings were positive for malignancy in 31 cases; histologic diagnoses included renal cell carcinoma (n=23), transitional cell carcinoma (n=5), and metastasis (n=3). Biopsy revealed 15 benign diagnoses: oncocytoma (n=6), hemorrhagic renal cyst (n=3), chronic nephritis (n=3), angiomyolipoma (n=2), and mycotic renal abscess (n=1). The average follow-up period for patients with benign diagnoses was 16 months. Biopsy results showed normal renal parenchyma in eight of 54 procedures, all of which had recuperated by subsequent biopsies. No immediate complications occurred after the procedures. Imaging-guided percutaneous core biopsy is a safe and accurate method for the evaluation of renal masses.

Partial nephrectomy for patients with a solitary kidney: the Memorial Sloan-Kettering experience

OBJECTIVE

To report the experience of partial nephrectomy in patients with a solitary kidney at one institution, with analysis of renal function, complications, oncological efficacy and survival.

PATIENTS AND METHODS

We identified 54 consecutive patients with a solitary kidney who had a partial nephrectomy between December 1989 and July 2003. Variables examined included patient age and gender, renal function, renal ischaemia time, surgical margin status and complications. Pathological features, e.g. tumour size, histological subtype and tumour stage, were also assessed. Disease-free probability and overall and cancer-specific survivals were determined.

RESULTS

The histological subtype was clear cell in 35 cases (65%), papillary in 10 (19%), oncocytoma in four (7%), chromophobe in two (4%), unclassified in one (2%) and multiple subtypes in two (2%). The median creatinine level before surgery was 14 mg/L, which increased to 16 mg/L 6 months afterward, and at 1 and 2 years after surgery it was 15 mg/L. Two patients developed end-stage renal disease requiring haemodialysis, one soon after surgery and another 8 years after nephron-sparing surgery. In all, 26% of patients developed at least one perioperative complication, with acute renal failure and urinary fistula being the most common. At 5 years the overall and cancer-specific survival, and disease-free probability were 68%, 88% and 73%, respectively.

CONCLUSIONS

Partial nephrectomy is safe in patients with a solitary kidney, with an acceptable decline in renal function and low likelihood of requiring temporary or permanent haemodialysis. After an initial decline, renal function appears to stabilize during the first year.

Characteristics of image-detected solid renal masses: Implication for optimal treatment

BACKGROUND

Solid renal masses are found increasingly. Further analysis of the characteristics of solid renal masses is useful for optimal treatment.

METHODS

A retrospective analysis of all solid renal masses was conducted from December 1998 to May 2003 at the Urology Department, Central University Hospital of Saint-Etienne, France. A total of 162 solid renal masses were treated. The preoperative imaging diagnosis of ultrasound and computed tomography, and final pathological results were reviewed.

RESULTS

One hundred and forty-five tumors were pathologically confirmed to be renal cell carcinomas (RCC); 17 tumors (10.5%) were benign. There were eight renal oncocytomas, eight renal angiomyolipomas and one benign mixed epithelial/stroma tumor. Three oncocytomas and five angiomyolipomas were strongly suspected before surgery. The majority of the benign tumors were < or =4 cm. The percentage of small benign tumors (< or =4 cm) was significantly higher than large benign tumors (>4 cm). Although it is possible to use imaging to detect some benign tumors, the majority of benign tumors cannot be diagnosed definitively by imaging before surgery.

CONCLUSIONS

Malignancy in solid renal masses is tumor-size related. Benign solid renal tumors appear mainly as small-sized tumors. The preoperative differentiation between an RCC and a benign tumor can be difficult. Our data suggest that a biopsy is necessary in selected patients to achieve the maximum accuracy in order to provide optimal treatment.

Prospective analysis of computerized tomography and needle biopsy with permanent sectioning to determine the nature of solid renal masses in adults

PURPOSE

We prospectively determined the accuracy of computerized tomography (CT) and needle biopsy of solid renal masses.

MATERIALS AND METHODS

A total of 100 patients with a solid renal mass who were scheduled for operation were prospectively evaluated. CT was performed before radical or partial nephrectomy. Biopsy of the surgical specimens was done twice through the tumor using an 18 gauge biopsy gun. Specimens were sent for permanent section and review by 2 pathologists blinded to each other and to the whole tissue specimens. Images were reviewed by 2 radiologists blinded to each other and to the results of pathological analysis. Results of CT and permanent biopsy were compared with the results of whole tissue specimen analysis.

RESULTS

Specimens were obtained from 59 radical and 41 partial nephrectomies. Malignant neoplasms were present in 85 patients (85%). Overall accuracy was 77% and 72%, the nondiagnostic rate was 20% and 21%, sensitivity was 81% and 83%, and specificity was 60% and 33%. For the 2 radiologists overall accuracy was 60% and 66%, the nondiagnostic rate was 31% and 23%, sensitivity was 70% and 77%, and specificity was 20% and 20%, respectively.

CONCLUSIONS

Overall permanent biopsy results were accurate in more than 72% of cases and CT was accurate in more than 60%. However, because the nondiagnostic rate for CT and needle biopsy was 20% and 31%, respectively, and specificity was low, we do not recommend routine preoperative CT and subsequent needle biopsy to guide treatment decision making. Rather, cases must be decided individually.

Partial nephrectomy: the rationale for expanding the indications

BACKGROUND

We report preliminary results of partial nephrectomy for renal tumors of > or =4 cm in 39 patients with the intent of extending the indications for kidney-sparing surgery.

METHODS

From July 1989 to October 2001, 39 patients underwent a partial nephrectomy for renal cortical tumors >4 cm in maximum diameter. Fourteen (36%) had the procedure performed for essential reasons, and 25 (64%) had an elective kidney-sparing operation. We evaluated tumor location and histology, perioperative renal function, and postoperative complications.

RESULTS

There were 20 conventional clear-cell (51%), 13 papillary (33%), 4 chromophobe (10%), and 3 oncocytomas (8%) with a median tumor size of 5 cm. After a median follow-up of 13 months, 36 patients had no evidence of disease, 1 patient had died as a result of other causes, and 2 patients who had essential operations were alive with disease. Twenty-three patients (70%) maintained normal postoperative renal function. Of six patients with moderate preoperative renal dysfunction, five (83%) had no change in postoperative renal function and only one patient required short-term dialysis.

CONCLUSIONS

With careful patient selection, partial nephrectomy can be effectively used to treat patients with renal cortical tumors >4 cm in diameter. The benefits of this approach include the effective local tumor control while at the same time preserving maximum renal function.

Temporal change in risk of metachronous contralateral renal cell carcinoma: influence of tumor characteristics and demographic factors

PURPOSE

To determine the relative risk (RR) of developing a metachronous contralateral renal tumor after an initial diagnosis of renal cell carcinoma (RCC), with stratification by renal tumor characteristics, demographic factors, and follow-up duration, in order to develop an improved risk-based surveillance strategy.

PATIENTS AND METHODS

The 1973 to 1997 Surveillance, Epidemiology, and End Results database was used to determine the observed and expected number of metachronous contralateral renal tumors developing after an initial diagnosis of RCC.

RESULTS

A total of 43,483 patients had a first diagnosis of RCC. Contralateral RCC developed subsequently in 155 (0.4%) of 40,049 patients with follow-up who had no synchronous diagnosis of RCC, with 10.81 expected cases (RR, 14.3; 95% CI, 12.2 to 16.8). The respective RRs (and 95% CIs) for contralateral RCC for white men and women were 16.0 (11.1 to 22.3) and 13.7 (7.7 to 22.6) at less than 2 years, 8.8 (5.0 to 14.3) and 10.5 (5.0 to 19.3) at 2 to 5 years, 13.5 (8.1 to 21.0) and 5.1 (1.4 to 13.2) at 5 to 10 years, and 13.0 (6.2 to 23.9) and 13.7 (5.0 to 29.9) at > or = 10 years, respectively. The RRs were significantly higher in black compared with white men for the first 5 years, with the RRs (and 95% CIs) in the former group of 95.3 (58.2 to 146.7) at less than 2 years and 41.9 (16.8 to 86.3) at 2 to 5 years.

CONCLUSION

The incidence of metachronous contralateral RCC is stable on long-term follow-up, suggesting that surveillance of the contralateral kidney should remain rigorous on extended follow-up. Black men are at a significantly higher risk of developing contralateral RCC in the first 5 years of follow-up.

Localized renal cell carcinoma

The last decade has brought dramatic changes in our understanding of localized renal tumors. Due to vast improvements in the abdominal imaging modalities of computed tomography (CT), ultrasound, and magnetic resonance imaging (MRI), approximately two-thirds of patients at our center have their renal tumors discovered incidentally. This tumor stage and size migration has vastly improved survival rates; more than 75% of patients with localized renal tumors achieve cure after surgical resection. In addition, the increased presentation of small, incidental tumors has increased the therapeutic options for urologic surgeons with surgical or tumor ablative techniques who now consider preservation of renal function as a goal equally important to local tumor control. Renal cortical tumors, viewed previously as a single type of cancer (ie, hypernephroma, renal cell carcinoma) with a uniform metastatic potential, are far more complex in nature. Renal cortical tumors are a family of neoplasms with distinct histological subtypes and distinct cytogenetic and molecular defects. Metastatic potential, once thought to be dependent only on tumor size, grade, and stage, varies according to tumor histologic subtype, ranging from the most potentially malignant conventional clear cell carcinoma, to the indolent papillary and chromophobe carcinomas, to the virtually benign renal oncocytoma. Surgical approaches to the localized renal cortical tumors now include the classic radical nephrectomy, kidney-sparing surgery, and innovative techniques that involve laparoscopy. New therapeutic modalities, such as renal cryosurgery and radiofrequency ablation, are under active investigation. Whether these new approaches to localized renal tumors will supplement or replace current surgical techniques will depend on the findings of carefully designed and controlled clinical trials.