Re: lung cancers, primary vs secondary

[epirad@mchsi.com]

Dr. Cohen, you ask "Why is this not a problem for cancer incidence which you 

say is  more reliable and for which autopsies are never possible?"



SEER incidence data are based not only on death certificates but often of other 

sources of more reliable information.  Because of the generally short survival 

of lung cancer, autopsy information is fequently availble for incidence data. 



Dr. Cohen, you asked, "What do you mean by surrogate? Why don't you specify 

that the issue is incidence vs mortality -- both data are from NCI? What do you

mean by poor agreement? What is the evidence that this is correlated with

radon levels on a national scale?"



The issue is not just incidence and mortality, but rather the quality of the 

state cancer registry that provides the data.  I previously told you that the 

SEER Program is the only comprehensive source of population-based information 

in the United States that includes stage of cancer at the time of diagnosis and 

survival rates within each stage.



See also -  http://www.seer.cancer.gov/



You ask what do I mean by poor agreement of your mortality data - 



The rank order of county lung cancer rates varies substantially over time 

periods.  This can be seen in Riggan’s county mortality data, used by Cohen, 

which exhibit little correlation across time.  For example, the 1960-1969 

county lung cancer mortality data for Iowa (Riggan et al. 1983) are in 

surprisingly poor agreement with the corresponding rates from 1970-1979.  The 

rank correlations are 0.398 for males and 0.163 for females.  In fact, at the 

5% level of significance, the correlation for females is not different from 

zero (p = 0.106).  Cohen (1995) only considers models in which the covariate 

effects on risk are linear.  Under this assumption of linearity, lung cancer 

rates will fail to correlate across time periods only if there is at least one 

risk factor for the disease which does not correlate across time.  The small 

correlations observed for his lung cancer rates indicates that this is indeed 

the case.  Cohen uses his risk factor information, collected after the lung 

cancer deaths, as if it was representative of earlier time periods.  Since this 

is not the case, he will not be able to control for their true effects on lung 

cancer risk.



Further - 



LUNG CANCER INCIDENCE RATES IN IOWA

	

All lung cancer cases diagnosed in Iowa are reported to the SEER State Health 

Registry of Iowa (SHRI) (Karnell et al. 1995).  Gender-specific lung cancer 

incident rates from 1988-1992 for individuals aged 40-84 were obtained from the 

SHRI.  The rates are age-adjusted by the total 1970 U.S. population.  Since 

lung cancer has a low survival rate, one would expect there to be little 

difference between incidence and mortality rates.  Nevertheless, in assessing 

the impact of risk exposures, it is more appropriate to use incidence data.  

The age range 40-84 was selected from the Iowa data because these individuals 

had a greater cumulative radon exposure in the time period following Cohen’s 

radon measurements, and because lung cancer is rare in individuals less than 40 

years of age.

	When we replicate the regression of Riggan’s lung cancer mortality data 

on Cohen’s radon measurements, we get the same large negative associations as 

reported by Cohen (1995).  However, this approach is flawed because it is based 

on temporally incorrect mortality data observed before the time of exposure.  

The results are quite different when we regress the more temporally correct 

Iowa SHRI lung cancer incidence rates on radon and smoking percentages.  The 

analysis produces spurious results – positive slopes for one group, negative 

slopes for the other.  In contrast, Cohen found negative slopes for both Iowa 

males and females.  Iowa's negative slopes were typical of the other 33 states 

in his study.  Among males and females, respectively, the slopes for Iowa 

ranked 18th and 15th overall.  We used incidence rates for Iowa since these 

data were readily available to us through the Iowa SEER Cancer Registry.  

However, the impact of using their data serves to underscore the importance of 

using current incidence data, rather than retrospective mortality data when 

studying disease risk factors.  



 

> >

> > More to the point, we have conclusively shown that the mortality data used by

> > Dr. Cohen is temporally incorrect in relation to the latency period for 

> cancers

> > and radon testing periods in Dr. Cohen's data.

> 

> 	--I have responded to this before, quite recently. If anyone wants

> a repeat, please ask.

> 

>  Actual incidence lung cancer

> > data from a National Cancer Institute Cancer Registry is in very poor 

> agreement

> > with Dr. Cohen's surrogate data for the time period of interest.

> 

> 	

> 

> 

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