Page 171 - 20dynamics of cancer

156 CHAPTER 8

1.0 0.8 (a) 1 (c)
Fraction surviving 0.6 0.4 Incidence 0.1 Mlh3

Mlh1
0.01
0.2
Pms2
Mlh3Pms2
5 10 15 20 2 4 8 16
1.0 0.8 (b) 5 4 (d)
Fraction surviving 0.6 0.4 Acceleration 3 2

0.2
0 1
5 10 15 20 2 4 8 16
Age in months Age in months

Figure 8.7 Age of lymphoma onset in mice with different mismatch repair
genotypes. For each genotype, both alleles at each locus were knocked out.
(a) Kaplan-Meier estimate at each age of the fraction of mice that have not yet
developed lymphoma among the population of mice that remain at risk. (b)
Smoothed curve fit to the estimated survival curve by the smooth.spline func-
tion of the R computing language (R Development Core Team 2004) with the
smoothing parameter set to 0.5. (c) Incidence of lymphomas on log-log scales.
(d) The acceleration of lymphoma onset calculated from the slope of the lines
in (c). Redrawn from Frank et al. (2005).

METHODS
Usually, the lab animals in each group have a common genotype and
common method of treatment. Each group forms a population in which
one observes the time to onset for a particular stage of cancer progres-
sion in a particular tissue. From the onset times, one estimates a “sur-
vival” curve, where “survival” here means time to onset of some partic-
ular event.
In each time interval, for example in each month, one has a listing
of how many animals were removed because they suffered the event of
interest and how many animals were removed for other causes. If we