TABLE 5.10

Summary of Studies Assessing the Volume-Outcome Relationship for Surgery for Pancreatic Cancer

Study

Study Years

Sample Size

Definition of Low and High Volume

Effect Size (mortality rate for low-vs. high-volume hospitals)

Patients in Low-Volume Hospitals (%)

Begg et al., 1998

1984-1993

742

1-5, >11

12.9 vs. 5.8a

53

Glasgow and Mulvihill, 1996

1990-1994

1,705

1-5, >50

14.1 vs. 3.5b

53

Janes et al., 1996

1990

8,917

<5, >20

7.7 vs. 4.2c

Lieberman, et al., 1995

1984-1991

1,972

<10, >81

18.9 vs. 5.5b

24

Sosa et al., 1998

1990-1995

1,236

<5, >20

14.7 vs. 1.9d

35

Wade et al., 1995

1987-1991

369

<1, >2

7.5 vs. 4.0e

a 30-day unadjusted mortality for pancreatectomy.

b Risk-adjusted in-hospital mortality for pancreatic resections.

c Unadjusted in-hospital mortality for ''curative'' procedures.

d Unadjusted in-hospital mortality for all procedures (i.e., resections, bypasses, stents).

e Unadjusted operative mortality for Whipple resections.

International Bone Marrow Transplant Registry. High transplant center volume was associated with lower treatment-related mortality among 1,313 transplants of human leukocyte antigen (HLA) identical sibling bone marrow for early leukemia (acute leukemia in first remission or chronic myelocytic leukemia [CML] in first chronic phase) performed from 1983 to 1988 (Horowitz et al., 1992). After adjustment for differences in patient and disease characteristics, the relative risks of treatment-related mortality (1.53, p < .01) and treatment failure (1.38, p < .04) were higher among patients who received transplants at centers doing five or fewer transplants per year than among those at larger centers. This lead to an absolute 10 percent difference in two-year survival (65 versus 55 percent) at the high-compared to low-volume centers. No differences were found among centers performing from 5 or more transplants to 40 or more transplants per year. One-quarter (24 percent) of centers performed 5 or fewer allogeneic transplants per year, and five (6 percent) performed more than 40 per year.

In summary, there is a large body of evidence to suggest that higher volume contributes to better outcomes for at least some aspects of care for some forms of cancer, especially high-risk surgery. The six studies that have assessed the way volume affects surgical outcomes of patients with pancreatic cancer are summarized in Table 5.10. Differences in how volume categories were defined, what procedures were assessed, and whether mortality comparisons were adjusted for case mix make it difficult to make simple comparisons of study findings. In general however, there is a two-to threefold increase in short-term postoperative mortality in lower-compared to higher-volume facilities. Although these differences may appear dramatic, they are not all statistically significant (e.g., differences noted by Wade et al., 1995). Furthermore, findings from observational studies must be interpreted with caution because they are subject to bias. In particular, differences in staging procedures and case mix associated with hospital volume could bias results in favor of higher-volume hospitals (e.g., referral centers tend to have a more favorable case mix). A relatively



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