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Renal neoplasms in younger adults: analysis of 112 tumors from a single institution according to the new 2004 World Health Organization classification and 2002 American Joint Committee on Cancer Staging System.

CONTEXT
Adult renal neoplasms have a predilection for older patients and are clinically and morphologically distinct from renal neoplasms found in pediatric age groups. Relatively rare tumors occur in younger adults (18-45 years of age). Whether these renal tumors are morphologically and clinically distinct from those of older adults has been the subject of controversy. Recent modification of the World Health Organization histologic classification and the American Joint Committee on Cancer staging system of adult renal tumors further highlighted the need for case analysis in this age group.


OBJECTIVE
To analyze renal tumors in younger adults based on a large surgical series from a single institution.


DESIGN
Of 780 renal mass nephrectomy (partial, total, or radical) specimens that were available for evaluation and had been obtained between 1986 and 2004 at Loyola University Medical Center, 112 specimens were from patients between 18 and 45 years of age. The tumors were reevaluated according to the 2004 World Health Organization classification and the 2002 American Joint Committee on Cancer staging system.


RESULTS
The likelihood of clear cell renal cell carcinoma was significantly reduced from 65% in older adults to 53% in younger adults (18-45 years, P = .04). The reduction trend was more significant when comparing an even younger age group. The majority (64%) of clear cell renal cell carcinoma in younger adults was low stage, T1a. Seventeen percent of these tumors had multilocular cystic features involving more than 50% of the tumor volume (55%-85%). The number of oncocytomas was also significantly lower in younger adults than in older adults (2% vs 11%, P < .001), and this presumably age-related benign neoplasm was not identified in patients younger than 40 years in this study. In contrast, the miscellaneous tumor category showed a remarkable increase, from 4% in older adults to 26% in younger adults (P < .001). The youngest patient group (18-35 years) had a higher incidence of miscellaneous tumors, 37%. Younger female adults tended to have more benign miscellaneous neoplasms than did their male counterparts (64% vs 36%, P < .001). Clear cell and chromophobe renal cell carcinoma occurred more frequently in younger male adults than in female adults (2:1 and 8:1, respectively).


CONCLUSIONS
Renal neoplasms are more heterogeneous in younger adults and have a different distribution pattern compared with that in older adults. Malignant and benign renal neoplasms tend to have a contrasting sex distribution in younger adults.