title: The natural history of incidentally detected small renal masses.
abstract: BACKGROUND
  The incidence of renal cell carcinoma (RCC) is increasing, largely due to the widespread use of cross-sectional imaging. Most renal tumors are detected incidentally as small, asymptomatic masses. To study their natural history, the authors prospectively followed a series of patients with this type of lesion who were unsuited for or refused surgery.
  
  
  METHODS
  Twenty-nine patients with 32 masses that measured < 4 cm in greatest dimension (25 solid masses and 7 complex cystic masses) were studied. The primary outcome was tumor size, which was calculated as volume over time. All patients were followed with serial abdominal imaging, and each mass had at least three follow-up measurements. The median follow-up was 27.9 months (range, 5.3-143.0 months).
  
  
  RESULTS
  Overall, the average growth rate did not differ statistically from zero growth (P = 0.09; 95% confidence interval, - 0.005-0.2 cm per year) and was not associated with either initial size (P = 0.28) or mass type (P = 0.41). Seven masses (22%) reached 4 cm in greatest dimension after 12-85 months of follow-up. Eight masses (25%) doubled their volumes within 12 months. Overall, 11 masses (34%) fulfilled 1 of these 2 criteria of rapid growth. Nine tumors were removed surgically after an average of 3.1 years of follow-up because it was believed that they were growing fast. No patient had disease progression.
  
  
  CONCLUSIONS
  Approximately one-third of small renal masses that are presumed RCCs grow if they are managed conservatively and are followed with serial imaging. The growth rate is slow or undetectable in the majority of patients. These observations raise the possibility of a period of initial observation in selected patients, particularly the elderly or infirm.
authors.affiliation: Division of Urology, Department of Surgical Oncology, University Health Network (Princess Margaret Hospital), University of Toronto, Toronto, Ontario, Canada.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Volpe
authors.forename: Tony
authors.initials: T
authors.lastname: Panzarella
authors.forename: Ricardo A
authors.initials: RA
authors.lastname: Rendon
authors.forename: Masoom A
authors.initials: MA
authors.lastname: Haider
authors.forename: Filippos I
authors.initials: FI
authors.lastname: Kondylis
authors.forename: Michael A S
authors.initials: MA
authors.lastname: Jewett
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D002292:Carcinoma, Renal Cell / Q000000981:diagnostic imaging / Q000473:pathology* / Q000601:surgery; D018450:Disease Progression; D005260:Female; D006304:Health Status; D006801:Humans; D007680:Kidney Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology* / Q000601:surgery; D008297:Male; D008875:Middle Aged; D009367:Neoplasm Staging; D011379:Prognosis; D011446:Prospective Studies; D011859:Radiography