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here a divergence occurs in recent years which reflects the movement of the lung cancer
ratio within the cancer group.
Incidence and
prevalence
While the facts about lung cancer mortality are relatively straightforward, it is
more difficult to assess the incidence and prevalence of the disease. As Doll (1953)
points out no figures are available for assessing the incidence of lung cancer other than
the Registrar-General's mortality figures, but because of its great fatality the number of
persons dying from it is nearly equal to the number affected and, from this point of
view, mortality statistics provide a reasonable estimate of incidence, although they are
subject to the inaccuracy inherent in the certification of causes of death.
Any such estimate of incidence to be of current application needs amendment in
the light of the time interval between the onset of the disease and death, which is in
turn affected by the effects of treatment.
Interval
between
symptoms and
treatment
Until the cancer registration scheme reaches a higher degree of completeness information
on timing can only be a guess and even if it were complete it would be less
reliable in the case of lung cancer because of the greater rapidity and fatality of this type
than of many other cancers.
However, isolated studies have been made of this question—Harnett (1952) shows
the number of lung cancer patients in the London hospitals during the years 1938 and
1939 distributed according to the interval from the appearance of first symptoms to
first consulting a doctor. There were 1,024 such patients of which 842 were males and
182 females, but in 216 of these cases no interval was recorded. According to these
statistics the average duration between the appearance of first symptoms and date of
first consulting a medical practitioner was, on the average, 78 days. In 80 per cent, of
these cases the interval was less than 3 months.
The same survey shows 417 of these patients distributed according to the duration
of symptoms at the time of commencement of treatment. According to the table, the
average duration was 171 days. The results of a later study by Edwards (1954) of a
small sample of 38 consecutive cases admitted to the Liverpool Thoracic Surgical Centre
were as follows :
Average
number No Less than 8 days Total
of days delay 8 days and over cases
Interval between onset of symptoms and
first visit to doctor 46.6 5 21 12 38
Interval between first visit to doctor and
X-ray of chest 55.8 2 11 25 38
Interval between first X-ray of chest and
surgical advice 46.7 0 9 29 38
Interval between surgical consultation and
admission to unit 9.6 3 19 16 38
Total 1587
It is not clear whether there is any difference in definition between the ' commencement
of treatment' in the London cases and the ' admission to unit' in the Liverpool
area, and in any case the longer time interval in Liverpool may merely reflect regional
differences in available accommodation, especially if incidence is rising also. The more
interesting fact is the reduction by about a month of the time between the onset of
symptoms and the consultation of a doctor. It is understood from Mr. Edwards that
the Liverpool study was carried out in 1953, from which it would be reasonable
to assume that, over the period of some 14-15 years between the collection of the two
sets of data, patients have become less unwilhng to seek medical advice at an early stage
in the onset of the disease. Possible reasons are numerous and it does not seem practicable
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