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To motivate the discussion in this chapter, we use the prognostic factor study concerned with patients with inoperable hepatocellular carcinoma conducted by Tan, Law, Ng and Machin (2003). The aim was to develop a prognostic index (PI), not the very best possible using sophisticated measures, but rather one of (easy) practicable utility. This study comprised two components.

In the first, several potential variables were investigated from information provided from 397 inoperable patients with hepatocellular carcinoma (HCC) who had all been diagnosed and treated at the same institution in Singapore (the index group). The variables considered included age, gender, ethnicity, significant alcohol intake, Zubrod performance score, presence of ascites, chronic hepatitis C, chronic hepatitis B, Child-Pugh Class, TNM Stage and serum AFP. From these 11 candidate variables, Zubrod score, presence of ascites and AFP levels were identified as prognostic. These were then used to derive a prognostic index, which allowed the HCC patients to be assigned to one of three risk (Low, Medium, High) groups.

The second component, applied the prognostic index so derived to 234 new HCC patients (the validation group) recruited to a multinational randomised clinical trial

Table 11.1 Characteristics of patients with inoperable hepatocellular carcinoma of the index and validation groups (after Tan, Law, Ng and Machin, 2003. Simple Clinical prognostic model for hepatocellular carcinoma in developing countries and its validation. Journal of Clinical Oncology,

Variable

Zubrod score

0

(ZPS)

1

2

3

4

Unknown

Presence

Yes

of

No

ascites

Unknown

AFP fog/L)

449

50-499

500-4999

5000-49 999

Gender Age (years)

Significant alcohol intake

Chronic hepatitis B

Chronic hepatitis C

Child-Pugh Class

Chinese Malay Others Myanmar Thai Others Male Female 439 40-49 50-59 60-69 70-79 580 Yes No

Unknown

Unknown

Unknown A B C

UICC TNM I/II Stage III

IVa IVb

Index

group

n

%

32

8

119

30

118

30

42

11

8

2

78

20

167

42

227

57

3

1

80

20

55

14

86

22

93

23

84

21

352

89

31

8

14

4

333

84

64

16

21

5

37

9

92

23

120

30

93

23

34

9

68

17

277

70

52

13

325

82

21

5

53

13

27

7

318

80

52

13

137

35

184

46

76

19

64

16

41

10

214

54

78

20

Validation

group

n

%

69

21

157

48

59

18

37

11

2

1

129

40

194 1 41

60

13

21

6

171

53

21

6

17

5

156

48

34

11

103

32

14

4

17

5

270

83

54

17

reported by Chow, Tai, Tan et al. (2002). The purpose was to see if the PI so derived was indeed prognostic for the disease.

The basic characteristics of the index group with respect to all the candidate variables and those eventally identified as prognostic are given in Table 11.1. The corresponding numbers of patients of the validation group are also included. It should be noted that fewer variables were recorded in the validation group as it is generally good practice to keep these to key variables so as to minimise the work for the clinical teams entering patients into a trial.

The process of developing a 'simple' model in this context balances practical with statistical considerations. Practical issues include using categories for serum AFP, classifying any unknown characteristics into the worst group, and rounding the regression coefficients to obtain the relative weights attached to each variable.

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Beat The Battle With The Bottle

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