Materials and methods
2.6 Grade 2id b
4 = 5 6 3 = 34 0.0 144 96 120 72 24 48 0
Interval between first and second operation (months)
Figure 3.2 Kaplan-Meier plot of interval between first and second operations against grade at progression (p = 0.001, Log Rank test).
Of the 130 available cases, 11 patients, whose tumours were grade 2 (6 cases), grade 3 (2 cases) or grade 4 (3 cases), were alive (or censored) at the last follow up. The median survival time in patients whose tumour was diagnosed as grade 2,3, and 4 at first operation is 51.1 months, 34.1 months and 22.5 months respectively (Table 3.8). The median survival time in each group was also categorised according to grade at recurrence/progression and this is shown in Table 3.9. There was a strong association between grade diagnosed at either the first or second operation and survival time. Patients who were diagnosed as having a grade 2 tumour at first operation survived significantly longer than those with a grade 3 and patients with a grade 3 tumour survived longer than those with a grade 4 (Figure 3.3, p <0.001, Log Rank test). In addition, patients whose tumours were diagnosed as grade 2 at the first operation and progressed to grade 3 and those whose tumours were diagnosed as grade 3 at the first operation and recurred at the same grade
lived longer than those whose tumours progressed to grade 4 regardless of their original grade (Figure 3.4, p <0.001, Log Rank test). There was no statistical difference in survival time between patients with grade 4 tumours who had only a single operation and who had two operations.
The correlation between grade and survival time was further analysed by splitting tumours into subgroups by grade at the second operation. Patients with grade 2 tumours which progressed to grade 4 had a shorter survival time than those which progressed to grade 3, although this difference did not reach statistical significance (p = 0.134, Log Rank test). This association is also seen in grade 3 tumours which progressed to grade 4 where these patients had a shorter survival time than those that stayed at the same grade at recurrence (p = 0.114, Log Rank test). Those patients with grade 4 tumours who had a single operation and those who had two operations had similar survival times.
Patients were divided into three age groups for further analysis (group 1: s40 years, group 2: 41 - 60 years, group 3: > 60 years). Several studies have shown the clinical relevance of using such subdivisions of age (Penman and Smith, 1954; Davies et al., 1996). The validity of these subdivisions has also been emphasised by the MCR Brain Tumour Working Party who have applied age (subdivided into three groups) as one of the prognostic variables used to stratify patients in subsequent clinical trials (Bleehen et al., 1991; Thomas et al., 2000). Patients who developed grade 4 tumours were significantly older than patients with lower grade tumours (p < 0.001, Student’s t-test). About 70% of patients with grade 2 or grade 3 tumours were 40 years old or younger, while about 60% of grade 4 patients were older than 40 years. Without taking tumour grade into consideration, patients
who were younger than 40 years of age survived significantly longer than those who were between 40 to 60 years old or who were older than 60 years (Figure 3.5, p = 0.002, Log Rank test). In addition, younger patients also showed a longer duration between first and second biopsies (Figure 3.6, p = 0.002, Log Rank test). However, when dividing the patients by tumour grade at the first biopsy, only patients with grade 2 tumours showed this difference in survival time (Figure 3.7, p = 0.035, Log Rank test)
Nevertheless, age did not correlate with the progression of tumours. There was no significant difference in age between patients with grade 2 tumours which progressed to grade 3 and those which progressed to grade 4 and there was no difference in age between patients with grade 3 tumours which recurred at the same grade and those which progressed to grade 4 tumours.
Grade at 1®* operation
Median survival time in months (range) 51.1 (7 .6 -1 4 7 .5 ) 34.1 (12.3 -1 6 4 .5 ) A 22.5 4 (1 .4 -3 1 6 .5 )
Table 3.8 Survival time and grade at first operation.
Grade at 1** operation
Grade at 2"** operation
Median survival time in months (range) 2 3 56.1 ( 12.1 - 1 47.5 ) 4 35.9 (7 .6 - 14 1 .6) 3 3 44 .9 (2 7 .3 - 164.5 ) 4 30.8 ( 12.3 - 5 7 .2 ) 4 4 22.3 (5 .0 - 3 1 6 .5 )
Grade 4 with a single operation 263
( 1.4 - 2 0 7 .0 )
Table 3.9 Survival time in each subgroup divided by grade at the first and second operations. 1.0 G ra d e 1st b*— “ 4 = 60 3 CO E 3 o o 3 = 26 Ü 2 = 44 0.0 48 120 144 survival tim e in m o n th s
Figure 3.3 Kaplan-Meier plot of survival time against grade at first operation (p < 0.001, Log Rank test).
I
3 CO E d Grade 2nd bx □ 4 = 59 □ 3 = 34 0.0 120 144survival time in months
Figure 3.4 Kaplan-Meier plot of survival time against grade at second operation (p < 0.001, Log Rank test).
1.2 1.0
I
3 CO E 3 o Age group “ > 60 yrs = 9 □ 41-60 yrs = 49 < 40 yrs = 72 0.0 120 144survival time in months
Figure 3.5 Kaplan-Meier plot of survival time against age group (p = 0.002, Log Rank test).
I
3 (/) E O Age group a 41.^0 yrs = 12 _ a < 40 yrs = 32 0.0 0 24 48 72 96 120 144survival time in months
Figure 3.7 Kaplan-Meier plot of age against survival time in grade 2 tumours (p = 0.035, Log Rank test).
. > 8 Age goup mm I ° > 60 yrs = 4 ° 41-60 yis = 35 0.0 < 40 yrs = 65 144 120 72 96 48 24 0
Interval between first and second operation (months)
Figure 3.6 Kaplan-Meier plot of interval between first and second operations against age group (p = 0.002, Log Rank test)
6. Incidence and frequency of gemistocytic tumour cells
For the cases with two operations, gemistocytic tumour cells were present in the first biopsy sample in 53 out of 95 cases (55.8%) and the proportion of gemistocytic cells ranged firom 1.1% to 38.9%. There were gemistocytic tumour cells present in 59 out of 95 second biopsy samples (62.1%) and their fi-equency ranged fi*om 1.8% to 65.3%. In grade 2 tumours, there were 18 out of 45 cases which had a gemistocytic cell component in the first biopsy sample. The number of cases that contained gemistocytes increased to 28 cases in the second biopsy sample. However, the median gemistocyte counts of the first and second biopsy samples were not significantly different. Twenty of the 27 cases diagnosed as grade 3 in the first biopsy sample contained a gemistocytic cell component. Although a similar proportion of tumours with gemistocytic tumour cells was found in the second biopsy samples of this group, the median gemistocytic count significantly decreased from 18.0% in the first biopsy sample to 6.5% in the second biopsy sample (p = 0.031, Wilcoxon Signed Ranks test). Fifteen (65.2%) of the first biopsy samples and 12 (52.2%) of the second biopsy samples of the 23 grade 4 tumours with two operations had a gemistocytic cell component. There was no significant difference in the number of gemistocytes between the first and second biopsy samples taken from grade 4 tumours. The mean gemistocyte count in this group increased fi*om 5.9% in the first biopsy samples to 10.3% in the second biopsy sample, the median values showed only a slight increase from 5.3% in the first biopsy sample to 7.3% in the second biopsy sample (p = 0.169, Wilcoxon Signed Ranks test). Of the 37 grade 4 tumours with a single operation, there were 12 (32.4%) with a gemistocytic cell component. The percentage of specimens that contained a gemistocytic cell component in grade 4 tumours with a single operation was significantly lower than the first biopsy sample of grade 4 that had two operations (p = 0.017, Pearson Chi- Square test). This data is summarised in Table 3.10.
Gemistocytic cell component
Grade 2 Grade 3 Grade 4 Grade 4