Document 6423475

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A study of the histological ceil types of lung
cancer in workers suffering from asbestosis
in the United Kingdom
- r . v * F. WHIT-WELL, MURIEL L. NEWHOUSE', AND.DIANE R.-BENNETT.
S
^ < ^
TUC Centenary. Institute cf Occupational-Health, London School of Hygiene and Tropical
~Medicine," Keppe! SlreeL London WC1 £ 7HT
Vhilwelt, F., Ncnhouse, Muriel, L . and Bennett, Diane R. (J 974). British Jcuntcl of Ir.d.atricl
Medicine, 31, 295-303. A A I toy- of the historical cell types or Sung cancer ir. workers suffering
from asbestosis in the United Kingdom. The present stcdy concerns ike predominant cell type
of lung cancer in workers w.'th certified asbestosis who died cf carcinoma of the lung in the
United Kingdom between 1562 -rd 1972. d r i e s ! dsta. necropsy reports, histological Sections, and in some cases pzraffm clocks were obtained from the nine pneumoconiosis panels
in the country £nd from hospitals where the- patients hid been treaied. Hisio-ogical analysis
was confined to '.he &S male sne nine ferrule esses in which adtq^jis postmortem tissue had
been obiafred. The number of female cases was considered to be too small to b« of value as a
separate, series. Amsr.j ;he males, ad-rcocarcir.oma was l!:e commonest i>pe of lung cancer
found ir. ?4 k n . Ir.fc.-maiion sbrcut the smoking habits of 69 of the SS men v»as obtained; all
had smoked at some i-tne. T.icre wis Unit difference between tr.i smoking habits cf any group
" whatever the eeli type of carcinoma. The riimc-jlty in fir.uir.g *• comparable series of noaaibes!os-*»posed individuals is pointed out. jt is the usual practice to hold a necropsy on any
patient when asbestosis has been certified wherever the place of death. This series therefore
has a wider basis of selection than 3ny hospital-based series.
Cigarette smoking can exert a carcinogenic effect on different parts o( the bronchial tree,
producing squamous cr oat-cslled i urrO'jrs prcxirnaliy and adenocarcincrna distaliy. Asbestos
dust ]>ingin distal parts of the lur.g may exert a eo-carcinogeiic probably a multiplicative
effect with tobacco smoke, producing adenocarcinoma of the distal part of ihe icspir*
alory tract
Lung cancer occurs much more commonly in
asbestos workers than in comparable populations
who have had no asbestos exposure (Doll, 1955;
SeJikorT, Churg, and Hammond. J954; Jaccb and
Anspach, 1965; Kcvhoase, JSu9; NiniiOiuC, Berry.
Wagner, and Ti.rcJc. 1972). However, SelikorT,
Chwg. and Hammond (19£S) have shown thai lung
cancer is rarely found in non-sntoking ssbestos
workers, and rccrr.! evidence(Berry, N'ewhouse.and
Turok, 1972) suggests lh3t asbestos and cigjreile
'RtsersM fur reprints IO Dr. M. L. N«*hi^ie.
smoke have a multiplicative carcinogenic effect. In
the United Kingdom Jury: cancer is not itself a
prescribed disease in asbestos workers, the granting
of industrial compensation being dependent upon
the presence of isbestcsis.
There have been very few studies of the cell-type
frequencies of lung ccnccr ir. these with asbestosis,
most accounts being based upon very small series.
Hucper (1966) collected published cases and fo^nd
an unusually high percentaje of adenocarcinoma.
Hourihaitt and McCsughey (1966) examined J7
cases and found that adenocarcinoma occurred with
298
^o o6i G i
*w«m u u p i w i n
••mi
A ftuJy of tUf hhio'zcgiral celi typts ofluiz: ranter in osbtuos workers
299
unexpected frequency. Spencer (19CS) slates lhat Kctomy specimen. In seme pestmcricx. eases there had
asbestos cancers lend lo be of the peripheral udenc- been previous su'clccl rcmov-l of the C'Riours and histocarcir.oma variety. On ihc o:hcr hand. Kreybcr^ Icrlca! sceticris cf these were aiso »\a;Ubie.
5cct:ons «.cre siair.cd only with hccmatoxvlx. 3.-4
{1965)considers1hat !unjt cancers caused by entiresmental factors such as tobacco sr.-.o!sC or asbestos eosin bat tomci:.-.ws tissues had been stained with van
Gicscc Perls', and mucin stains.
dust tend u> be squamous or oat-ccll carcinomas,
and recently Kannerstein and Churc. (1972) have Clasvificaliua of tuir.t-.irs
found n o difference in the ec'il-lvpe frequency in a The his'.ctoplcal ci;ssii";ca:ion of lung tumours used was
series of lung cancers in asbestos workers combated a sixpiilted form of the World Health O.-car.isation
with lung cincers in non-asbestos-exposed indivi- classification and h;s been used previously in a surrey
- d u a l s in whom the cancer was presurr-ably.cisareUe-. _ Of lung cancer in Liverpool (\Vhit*ci; 19ila. b). In this
classification squamo-is lu'mours are' so'called only if
induced.
This conflict o f opinion as to ihe predominant tumour cells are seen to be forming keratin or fortninj
priefcie cc:i»; ac^.-.-jcircir-omas reveal acinar structure
cell type of lun? cancer associated with asbesiosis ar.d cr m-jcin secretion. A esse of malie-ant pulmonary
has stimulated the present i'>-iy. which has been adenomatosis or aiveo!ar<e!i carcinoxa w-cs cro-jped
concerned with assessing the significance of the ceil- with the adenocarcinomas. Oa:-celicarciROx.asall showed
type frequency found in a large series of workers the characteristic scull ova! n^cje; in eosinophilic cytosuffering from asbesiosis who died of lunj cancer.
piasMv which rsrely showed cell margins, and these
tjmoursscnelimes snowed aci-sr formation. Carcinomas
with none cf these features were classified as carcinoma
Present inttsligalioo
simplex, in which gro-p also were included i."art«ll and
In the United Kinjdorri workers suspected of having clear-cell carcinomas. To.-noJrs show inj a rnixed cellular
asbesiosis are referred 10 pricimccoitiesis medical panels pattern were grouped tojether as such and were mainly
which ire situated to Lo.-.don, the major jndasuial ader.osquar.ous catcino.-nas.
Where a tamcar was Ur£t!y undiiTe.-er.tiated but eoncentre? in E n j ! and and Wales, and in Glasgow in
Scotland. The worker is examined clinically ard radio- tained some differentiated arses it was grouped accordirqf
logical!}" and his pulmonary function ise-.aluated. If the to the duTerenliated tissue.
panel confirms lite cla.nosts. he h certified as suffering
from asbestosis and becomes ei:jible .for eomj-ensaiion. Grndinu cf asbesiosis
He is re-examined and reassessed annualiy and a: death It his bjen assumed that at postmcneiR exax.inations
is the subject of necropsy foliated by a coroner's inquest. the lung tissues selected for nncroscopic esarr.i.-.aiion had
It is the usual practice for panels to pieserve a!i ciir.:cal been taken from the rr.osi severely 3ffe::ed areas.
records o f these patients together with rcdicjrcpfcs and The lu.-g tissues hive Leers graded as follows:
r.ewopsy repels, and cTten histological sitdes from sur- 1. Normal: AsUs:o> bodies w-tre w-aliy present ia
srrail or nsodtrsie numbers bjt were within the
ji^al or necropsy specimens.
bronchioles 2nd distal air-spaces with no interstitial
In the present invesiication we were fortunate in having
fibrosis.
access to lists, compiled by the then Medical Division
of the Department of Employment (now the limploytftcn: 2. Miid si'ccstcsis: A similar number of asbestos bodies
was present but many of these weie in the inlerMedical Advisory Service) of 2ll deaths from Jung cancer
Stitial thsues cf the lurg where there w-a» slight,
occurrint, in those suffering from asbesiosis ss certified
often focal, interstitial fibrosis with seme irregular
by the pneumoconiosis panels between 1962 and 1970.
emph>sema.
Wc circulated these lists to the various panels with requests for the loan of clinical notes, necropsy reports, and 3. Moderate asbesiosis: Usually mare asbestos bodies
were present and the la-.g tissue shewed extensive
any histological slides.
ir,:ersti:ial fibrosis with oblileration of alveoli,
Tfee total material of (his study consists of the cases
cystic dilatatlsn of bronchioles with epitheiia! hyperreceived from the pr-comoconissis radical panels occurpiasia, irregalar emphysema, and co'Jaie-c^i
ring between 1962 and iS70, additicral eases front
pleural ihicljer.ine.
Scotland from 1970 until the er.d of J 972. and a further
23 patients *:so had worked at a London East End 4. Severe asbesiisis: The numbers of asbestos bodies
present were variable, being usually numerous.
asbestos factory ar.d had died of 1-jng cancer, al! but
Fibroses was advanced to a degree where it was
three of vshora suiTere:1 from certified asbesiosis (NewdisViCuli to rcco;riire the tissue as l^r.f. There was
house, 1969/. The clinics; rotes were nbstracted. ar.d
frequent cystic dilatation cf bronchioles wilh adenowhere necessary further in'ormction abcu: past occupaKiatcus and sc/ja.v.ous rrelaplasia. frretular emphytions, srr.ctinj habits, bronchoscopy, radtofraphs, ard
sema and pleural coltas;er,izat:o.-> were usuzliy
blstopatholojy were sought frcm the hospital where the
present.
patient had beer, treated.
Pathological mefcriat
The material ccrsisted of histological sections and scineflmes paraffin blocks of lissLe which had been prepared
mainly fro.T. postmortem c*am:"V3i:cns but occasionally
from fcror.ebial bicpiies, ar.d lobectomy and preurno-
Results
Of the 197 patienis listed, clinical and pathological
material was obtained in 545 cises ( 6 6 / 0 . The
>>5 F. ti'i'uiHv/f. Mtnicl L. .Wa/wuf, wJ Oiane R. Bcwxtt
TABLE 1
PRELIMINARY ANALYSIS OF SrFClMINS
Melt
Fema'e
Tc.M,'
23
10
It
M
2
2.<
i;
12
97
irnitq^llc jnaitria!
MtscihdiOTj or other tumour
Opetuim uus.t ott'y
&*liifj;:ory pcHCortcm (issues
Tout cajej examined
t
9
j 122 I
13 J Hi
results of ihe preliminary sorting arc shown in
Tfblel.
- In the'eases grouped as inadequate there was insufficient tumour tissue in the sections obtained at
biopsy or operation or from subsequent necropsy to
be aWe 5o consider it representative of the nsain
tumour.
There were 11 cases uhere the appearances were
' not those of a primary lung cancer, seven of them
probably beir.5 mesotheliomas and the others seco.-.dary carcinomas.
For these reasons the histological analysts has been
confined to the 97 esses where there was adequate
postmortem tuniour tissue end, except in two cases,
adequate lung tissue. The number of female cafes
is too small to be of value as a separate scries, and as
the histological cc!!-t>pe frequency In women may
differ from that found in men the feina'e casts have
been listed separately to avoid one factor which
confuses celi-lvpe frequency studies. This has Jeff
TABLE 2
HISTOLOGICAL TYPE or TUMOUR
Molt
%
Sqtunoux
o*t
Adenocarcinoma
Simplex
Mii*«S
19
23
30
12
4
21-6
26-1
J4-I
13-6
4-6
Total
M
Ftn-oU 7c::l
—
21
25
33
13
4
9
97
2
3
3
1
88 ms!c asbestos luna cancers for analysis. Ths
histo'cgical typing ol' the lumnurs is shown in Table
2 with the pcrccr.tacc Uiuribuiion of the male cases.
Adenocarcinoma was the commonest type of lunt
cancer, fotnd in 34% of cases.
Jf asbcs:osis hss any ni1ucr.ee on the cell-lyre
frequency :r. thv scries it is likely that this would be
shown by comparing the ccli-iypc frequency jn the
less severe -ase» of asbestosis with the more severely
affected. J.i "-'..b'c 3 the ceii'type- frequency of .the
cases with norma! and.mi'd asbestosis is compared
with thai found in those with moderate and severe
asbestosis. Two cases nave been omitled where there
•was inadequate lung tissue" ic classify by the type
of asbestosis. The table shows that in norma] and
mild asbestosis 2S% of the tumours were adenocarcinoma, whereas in the more severe asbestosis
3S % of the tumours were adenocarcinoma. However,
this difference was not siatbtically slzpiSsant. . ,.
Site of tumour
An attempt Has made to assess whether the tumour
arose in the upper or lower lobes and centrally or
peripherally, usir.j necropsy reports fc£«her with
reports of straight radiographs, tomography, bron*
choscopy, and surgery. Jn 65 of the series there was a
c!tar indication of the lebe cf origin; 19 (63%) of
the 30 tumours classified as adenocarcinoma and 32
(55%) of the other eel! types of the tumour appeared
to originate in cr.e or ether lower lobe. In 75 cf the
mate seres i! was possible to make a j-j^gment
uhether the '.un-.o'^r was central or peripheral in
origin. Of the adenocarcinomas, 15 (^0%) were
described as peripheral compared to 16 (27%) of the
tumours of other histological types.
Other features of the series
During the examination of pneumoconiosis panel
notes and hosp.'tal records (he opportunity was taken
to note smoking habits and certain other aspects of
the disease.
TABLE 4
SMOKING HABIT BY CFLL Type
TABLE 3
HISTOLOGICAL TYPE o r TUMOUR IS*
S6 LUNGS GRADED BY Stvsttm OF ASBESTCSJS
CtUiypt
Ncri>zr' L*g end
rA'J Oi&fttctii
Ss.
Oat
Adteotairi.'iomi
Oiitr
t
7
7
6
hiiit
st'tre
csbruosl:
Nor.-wnoier
Ex-Knoker
< F0 cigarette]
10-20 <ijirc;:«s
23 -r dcitcitn
II
16
22
9
19-0
2J-6
37*
15-2
S.-noli.-.g habit
1. covin
SmaxL-g hshli
not k.-.owo
%
2»6
25-0
25-0
21-4
Sn.iJ.ing
Sfjzr-.cxt and
Adt*o~
Other
Ton!
0
6
8
12
*
0
3
5
7
7
0
2
J
7
3
0
11
14
26
It
34
22
13
69
3
19
1
1
W jftJ>- oj the lauiiogittii cell y/vr ofh:-s cv,zcr in atbtsios -a&kerx 301
LalySJS.. The
k\n in Table
1 malc.cascs.
yrcof lung
lie ce)l-l>pe
liiuo'uld be
|cncy in ihe
*c severely
cncy of. the
. compared
I and severe ..
v here'there "
[»y die type
jicnnal and
I ere adenoabestojis
k. However,
fica.1t.
Ihe fumour
Centrally or
^her with
Iphy, brooIthere was a
{«%) of
Vrat w d 32
\ r appeared
175 of the
. judgment
ripheral in
}OJi) were
•7%) of the
losis panel
f- was taken
I aspects of
l**r Teud
P
f
»
7
3
0
11
M
2«
tt
69
*
1»
TABLE 5
SOME FEATURES OF PATIENTS WITH TUMOURS OF DIFFERENT CFLI, TYPES
CtUupe
AdtcocarcinotTH
Other
Age a '/•til txpciue
Aft a: dts:h
Ltirtit prrUx,
LfK?:h aftxpi.i*rc
No.
Meo*
Ac.
Mca*
he.
Mum
St.
IT
21
2J
14
2M
29-6
3<?|
2*3
19
23
30
16
«-7
J7-6
3?-*
56-3
17
2!
27
14
3J«
29-3
IS-7
27-9
II
23
»
14
'
Uraa
tS-9
21-2
21-9
22-9
t
.Smoking habits The smoking habits of 69 of the SS disease, is felly representative of lung cancer in those,
men in the scries had been recorded (Table 4). All wii'n certified asbestosis as i: is the usual practice for
the men had smoked cigarettes, though three hid coroners in England and ine pneumoconiosis panels
given up the habit over 20 vears before death and is Scotland to arrange a necropsy, and this applies
eight others had given up more reeer.tiy.
whether the patients die in hesphai or n their
Though the numbers are small they do not suggest homes. The scries clearly does not con'.ain all subthat the heavier cigaretie smokers were liable to any jects having certified asbestcsis and lung cancer who
particular cell-type of lung cancer. Sixty-seven per died in the United Kingdom in the period surveyed,
cent of the patients with squamous and cat-cell but those not included must have been emitted ooly
carcinomas were moderate or heavy smokers, v.hiie because of administrative errors in net notifying
the corresponding figures for those with adeno- cases to the authorities at death, not holcing necropcarcinomas and for the other cancers were 64% ar.d sies, losing records, or because pathologists took
inadequate histological sections. Ncr.ejof these
errors is likely to ha^e occurred more often with any
;
Age at first exposure In the different groups the particular cell-type of tumour.
mean age sifirstexposure varied only between 28 and
We consider thai 8S cases form a large enoogh
31 yeais. A quarter of the men in the series had serbs to provide a reasonable assessr.-.en: cf the
started to work with asbestos between the aces of 14 carcinoma cell-type frequencies occurring in certiand 18. but nearly onc-nfih had no; been exposed fied asbcsiosis. Many patients with certified ssbestountil over the sge of 40 (Table S).
sis have severe lung tiisccse and it may be that iung
cancers in early ari siight cases of asbcitcsis are not
Age at death This was known for ail patients, and adequate!}' represented, so any carcinoma cell-type
the mean age at death for the different cell-types is relationship with ?.sbe»!osis is likely to be exagalso shown in Table 5. The figures are very similar gerated jr. this seri-.-s.
lo these found in cases of ncn-asbesics lung cancer;
The real difficulty lies in finding a comparable
patients with ozl-ce'A carcinoma usually die about series of non-astestos b-t presumably cigarettefive years younger than those with squamous car- induced Jung canc-trs for comparison, and this seems
to be insuperable. Most reported large scries of lung
cinoma.
cancers contain a hii> proportion cf cases where the
Latent period This has been cakriated as the histological diagnosis i; based upon bronchiai biopsy
irsean cumber of years between first exposure and sp:>cimens, so that they rcf.ecl the high incidence of
death, end in the different groups varied between squamous and oal-cc!l tur=:ours in the larger accesi:b!e brcr.chi but igr.orc the rnor« inaccessible
27-3 and 33-2 years (Table 5).
peripheral adenocarcinomas Tnis can be seen ir. the
Duration of exposure Apart from three m»n with papers by Wyr.der and Gral-am ('$50) arid by Doll
squamous-ccll tumours -whose period of exposure and Hill (1964) referred to lai.tr. On the other hand,
was recorded as less lh3n two years, all hid been scries based upon surgically resected specimens
exposed for rr.ore than 10 years. The mean duration i.-.clude a high proportion cf squamous tumours,
of exposure varied between 17S years for those with because they are more likely to tx. resectable, and a
squimoiis-cclicarcinomato2)-9yeirsior those wish low proportion of cil-ccll carcinomas and acenoadenocarcinoma. The difference was not statistically corci.-.orms beca-jse these are mere jftcn found to be
inoperable. Ail postmortem series from scuic hospisigniiicant.
tals are influenced by the facts that patients with
known inoperable cancer lend iO be discharged
home or to a chronic sick hospital. aRd hcsoital
Discussion
necropsies are often held only when the clir.ical
This sciit?, unlike most postmortem studies of the
- «*-- . * - v » - v h
3iil
.. WwrfAVi. k . - t . L " - >
i
F. li'/J/K-f//, MurUlL. Xwteuse, crj DSu-x A'. Ikimru
TABLE 6
CELL TYPES IK MALE LUNG CANCER. BROADGRKN HOSPITAL, LIVERPOOL. 1950-60. IN
THHEE SERIES
Crtl Ijrpe
SMjuimou*
Oai-ctll
.,
'
£ « * . - » / bsf?n ttr'.ct
So.
379
IS
167
41
lttiel1
0?rte:.v. spc.'^n
*/
A<s.
41-1
3JT
2-0
18-1
32
107
77
142
24
923
Keeropty
strits
So.
17
38
29
12
7
37-J
131
94
17-4
29
*I5
t*-5
36-9
27-2
61
101
*1
•1
•When optratioa* fo.:o»ed broainsat biopty ihe cue is ss&idei only u*. Ihe optniiir. series.
diagnosis is uncertain. For these rcasor.i a lung
cancer necropsy series includes few of the more
. .easily diagnosable proximal bronchiai tumours such
as squamojs carcinomas, b-il it contains a high
proportion of adenocarcinomas, which are less
easily diagnosed and ofl:.. r reseni first with symptoms from their metastases.
Thesepoip.tsarede.T!orjstr3:edin Tab*e6, which has
been prepared after removal of female cases from
material already published (Whitwcll, 1561 b) on
cases occurring in the Liverpool area in one hospital.
The tabic shows the frequency of adenocarcinoma ia
the biopsy series to be 2%. in the opera tier, series.
9-5%, and in the postmortem series 23%. These
cases \xere probably mainly cigarette-induced carcinomas and in nor.e was asbciiosis fou::d, but Liverpool-is anarea where I0%ofcdu]ima'.esshc.¥pleufa!
piaq-jes at necropsy, ar.d where pleural mesotheliomas are relatively common (Whitwell and Ra'vcliife,
1971), so it is probable that if these Liverpool cases
are used as a control series they may well underestimate differences between asbestos-exposed ar.i
nor.-asbestos-expesed populations. There is r.o i r «
indication of the overall frequency of adenocarcinoma i.i an unseiected population but probably the
figure lies between 15 and 2u%, which is about ha^f
the frequency ue hate found in mare severe asbes-
among 17 male asbestos carcinomas, or about 35%,
On the other har.d, Kannerstein and Churg (1972),
in a study cf 50 lung cancers in asbestos workers,
found a frequency of 22%, which was « r y similar
to their control series. Hosvtver, iheir series was a
mixture of cases diagnosed by bron-chial biopsy,
secondary deposit biopsy, operation specimens, and
postmortem tissues, ar.d it is difficult to assess the
significance of fir.dings based upon such variable
material.
Our study has emphasized the important factor of
cigarette smoking in the development of asbestos
lur.j cancer, supporting the viem-s of Sslikoff ei al
(196S). Retrospective studies rely upon clinical notes
made leng ago in case-records, and though routine
notes concerning smcking habits can be misleading
they usually tend to underestimate the smoking
habits of patients. In the present series (here were
no patients who had i.'-i smoked cigarettes at some
time, and 64% had been moderate or heavy smokers
all their lives. There was no significant difference in
the smoking habits of patients with different ceiitypes of lung cancer.
It is wideiy held that squamous and oal-celi caretnomas of the lung are th; types caustd by cigarette smoking, while adenocarcinomas are unrelated to this habit, an opinion largely derived from
lOSiS,
the studies cf Wynier and Graham (1950), De'l and
Comparison of the present ^testes cancer series Hill (1954), and Kreyberg (1552, 196$). Among
with the earlier Liverpool series has the advantage Wynder and Grahams* series of 644 male carcinomas
that the same diagnostic criteria and classification there were only 39 adenocarcinomas, and the authors
ha-ve been used, and interpretation has been by the considered that they had not seen a suffici nt number
same pathologist
of adenocarcinomas io decide whether they conOur finding of an overall frequency of 34% of tained a higher proportion of chain-smokers than
adenocarcinomas in the lung cancer of certified was seen in the control patients. Dcil and Hill found
asbeslosis, ar.d of 3S% in the severely affected lungs 33 adenocarcinomas in their series of 916 lung
(Table 3) is higher than in most scries that have been cancers and there was no statistical difference in the
published. Hueper (!S66) fou.-.d 39% of adenocarci- amounts smoked by patients with tumours of differnomas among 104 published cases and compared ent histological grGuns, but they though: that the
this with 9-5% in ms'e controls. Kourihar.e and number of adenocarcinomas was too small to conMcCaughey {1966} four.d six adenocarcinomas clude that no diiTercnce existed. In 1964 these authors
l
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•
•
•
y
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^
m
m
m
m
' m .i'iig»
A study oj //«• hhiolfi
reported a prospective study of lung cancer in
British doctors, from which they concluJcd thct
there was n o marked cssoci-ition of sneckinc with
adenocarcinomas, but this scries included on!y 13
adenocarcinomas, Krcybcrg (1962; I96S) censiders
that JURE cancels due to external carcinocens such
as cigarette smoke and asbestos dust are -mainly
squamous and oat-ccll tumours, end thai adenocarcinomas are endosonous growths which have no:
risen greatly in their frequency in this century. His
opinion is partly based upon re-cxaminjtion and re"classif.ratidn "of rnaisriai already studied by Do!and Hill, but in his later work (Kreyberg, 196S) he
admits a threefold increase :rt the incidence of adenocarcinoma in cigarette srr.ofcerv compared with nonSmokers.
The Opposite view has been given by Ashley and
Davfes (1967) in a study of lung cancer in men from
south Water. Among 442 cases for which smoking
histories were available there were 50 adenocarcinomas, and cigarette smoking was foynd to be
associated wish adenocarcinoma as ofter. as with
ether types of iurtc cancer. They concluded that the
h i s t o r i c a l t)pe cf tumour depended entirely upon
which part of the respiratory tract was affected.
It is probable that ciga-ette stroking can exert a
carcinogenic effect upon different parts of the
bronchial tree, usually producing squamous or oatcell jurjiaurs when the m e r e proximai areas are
affected, ar.d adenocarcinonias when distal parts are
involved. As the concentration of carci.-.cgen is
likely to be higher in the more proximal parts of
the bronchial tree it is t o be expected that sc.uarr.ous
ar.d oat-cell tumours wili be most common with
cigarette-induced carcinoma. However, when asbestos dust, which reaches the distal parts of the bronchial tree, acts as a co-carcinogen with c»°axetie>
smoke, it is not surprising t o And that the maximum
carcinogenic effect, probably a multiplicative one,
produces adenocarcinoma in the distal part of the
respira'ory tract.
We uish to (hank Dr. Waikins Pitchfo.-d, Dr. R. M.
McCoMii). >ne doctcrs of the pnsun-.occn-c^'5. panels,
and Dr. W. Buchanan of the Department ofET.pIojroent
for their assistance and co-operation, ar.d Dr. J. C .
Gilicr. and Professor R. S. F . Schilling for (heir interest
and advice.
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