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© The Author 2007. Published by Oxford University Press.
CORRESPONDENCE |
Re: Rising Incidence of Small Renal Masses: A Need to Reassess Treatment Effect
Affiliations of authors: Division of Cancer Epidemiology and Genetics (WHC, SSD), and Center for Cancer Research (WML), National Cancer Institute, Bethesda, MD
Correspondence to: Wong-Ho Chow, PhD, Division of Cancer Epidemiology and Genetics, National Cancer Institute, 6120 Executive Blvd, EPS 8100, Bethesda, MD 20892-7240 (e-mail: choww{at}mail.nih.gov).
The trends in mortality rates according to tumor size for renal cell cancer (RCC) patients that were calculated by Hollingsworth et al. (1) are misleading because most RCC patients survive beyond the year that they are diagnosed. The prolonged survival means that the mortality rates for patients diagnosed during a confined period (1983–2002) should be low during the initial years and increase over time as more patients diagnosed during the early years die. In Table 1, we present two sets of total mortality rates based on data from the Surveillance, Epidemiology, and End Results (SEER) incidence-based mortality file (2)—one set for cases diagnosed during 1983–2002 (henceforth referred to as the restricted period) and the other for all cases diagnosed since the beginning of the SEER program (1973–2002, henceforth referred to as the whole period). Using the restricted dataset, the total mortality rates increased from 1.6/100000 in 1983 to 6.5/100000 in 2002, an increase of nearly 300% that is comparable to that reported by the authors. In contrast, based on the whole dataset, the increases in total mortality rates during 1983–2002 were much smaller, from 4.6/100000 in 1983 to 6.8/100000 in 2002, a 48% increase. The discrepancy in the increase in mortality rates was mostly due to higher mortality rates during the 1980s in the whole dataset relative to rates in the restricted dataset; the mortality rates in later years were more comparable. It is noteworthy that the mortality rates for patients with tumors of unknown size in the whole dataset declined steadily during the same time period, while rates in the restricted dataset stayed relatively constant. The difference in the trends was due mainly to omission of case subjects diagnosed before 1983, for whom information on tumor size was not available, and the declining contributions of these subjects to subsequent deaths over time. Similar discrepancies in mortality rates between the whole and restricted datasets emerged when only deaths due to kidney cancer were included (Table 1).
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Compared with mortality rates, survival rates should more accurately reflect the clinical course of patients following cancer diagnosis. We estimated survival rates for RCC patients diagnosed during 1983–1987, 1988–1992, 1993–1997, and 1998–2002 using the most recent SEER data file that included follow-up through 2003 (3). The 5-year relative survival rates improved consistently over time for RCC patients, from 56.4% for those diagnosed during 1983–1987 to 68.9% for those diagnosed during 1998–2002 (Table 2). The improvement in survival was most prominent for patients with small tumors: 5-year relative survival rates improved from 63.2% to 91.5% and from 78.3% to 88.8% for patients diagnosed with tumors less than 2 cm and 2–4 cm, respectively. Survival for patients diagnosed with larger tumors showed little improvement over time.
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Given the authors’ concerns regarding a disconnect between improved kidney cancer survival and continued rising mortality, it is worth noting that both incidence rates and survival patterns contribute to mortality rates. In general, mortality rates do track incidence rates, but the connection diminishes as survival improves. With the rapid increases in RCC incidence, it is not surprising to see an increase in kidney cancer mortality as well. However, mortality rates have leveled in recent years (4) as survival has improved.
Finally, we were puzzled by the authors’ choice of tumor histology codes to identify kidney cancer patients in their analysis. They included International Classification of Diseases for Oncology, 2nd Edition, histology codes 8960 (Wilms tumor) and 8963 (rhabdoid sarcoma) and nonspecific histology codes such as 8041 (small-cell carcinoma, not otherwise specified) but excluded codes that are clearly RCC, such as 8340 (papillary adenocarcinoma) (5).
REFERENCES
(1) Hollingsworth JM, Miller DC, Daignault S, Hollenbeck BK. Rising incidence of small renal masses: a need to reassess treatment effect. J Natl Cancer Inst (2006) 98:1331–4.
(2) Surveillance, Epidemiology, and End Results (SEER) Program. SEER*Stat Database: Incidence-Based Mortality—SEER 9 Regs Public-Use, Nov 2004 Sub (1973–2002)—Linked To County Attributes—Total U.S. 1969–2002 Counties, based on the November 2004 submission, released August 2005. Bethesda (MD): National Cancer Institute, DCCPS, Surveillance Research Program, Cancer Statistics Branch. Available at: http://www.seer.cancer.gov. [Last accessed: December 1, 2006].
(3) Surveillance, Epidemiology, and End Results (SEER) Program. SEER*Stat Database: Incidence—SEER 9 Regs Public-Use, Nov 2005 Sub (1973–2003)—Linked To County Attributes—Total U.S. 1969–2003 Counties, based on the November 2005 submission, released April 2006. Bethesda (MD): National Cancer Institute, DCCPS, Surveillance Research Program, Cancer Statistics Branch. Available at: http://www.seer.cancer.gov. [Last accessed: December 1, 2006].
(4) Chow WH, Devesa SS, Warren JL, Fraumeni JF Jr. Rising incidence of renal cell cancer in the United States. JAMA (1999) 281:1628–31.
(5) Percy C, Van Holten V, Muir C, eds. International Classification of Diseases for Oncology. (1990) 2nd ed. Geneva (Switzerland): World Health Organization.
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J Natl Cancer Inst 2007 99: 570-571.
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