(CANCER RESEARCH 26, Part 1: 514-518,March 1966]

possible contributing factors, and describe and illustrate themicroscopic appearance of the tumors.

Materials and Methods

All tumors in this series of animals, whatever their origins,were recognized initially by the changes they caused in shape,color, and texture of the organs and sites in which they developed. Diagnosis and classification have been guided by acceptedcriteria (5).

Statistics were prepared for each family of mammals and birdsrepresented by at least 1 lung cancer. Two potential sources oferror are recognized : diagnosis and selection. Errors in diagnosiswould increase frequency of occurrence either by includinglesions that were not cancerS or that were not primary in thelungs. Errors in selection would decrease frequency of occurrenceby failure to recognize a lesion macroscopically and save tissuefor microscopic examination. We will attempt to determine theprobable degree of these errors in presenting these records.

Age is expressed in months and represents exhibition periodsin the zoo. A majority of birds and mammals are placed in thiscollection as juveniles or as young adults; thus exhibition periodsin most instances approximate actual life-spans.

Observations

FAMILIES INVOLVED. Pulmonary cancers were found in 7

families of mammals and 4 families of birds as follows: Canidae—foxes, wolves, and other doglike animals; Felidae—lions,tigers, leopards, and other cats; Mustelidae—mink, skunks,otters, etc. ; Viverridae—civets, genets, etc. ; DidelphiidaeAmerican marsupials, common opossum; Paramelidae—Australian marsupials; Capromyidae—aquatic rodents; AnO.&Laeducks, geese, and swans; Phasianidae—pheasants and quail;Cathartidae—group of vultures; and Ploceidae—smal! passerinebirds.

CLASSIFICATION. Table 1 lists each animal, its exhibition

period, sex, and the type of lung cancer found. These tumors areall considered malignant and derived from epithelium. Theterms—adenocarcinoma, squamous cell carcinoma, and undifferentiated carcinoma—refer to the predominant microscopicStructure. Adenocarcinomas were relatively well-differentiatedtumors that formed glandular structures. The cells resembledthe epithelium of the bronchi, bronchioles, or the bronchialglands. Squamous cell carcinomas were tumors in which thepredominant cells resembled squamous epithelium and were

Summary

Postmortem examinations at the Philadelphia ZoologicalGarden have been continuous since 1901 and by December 31,1964, included records on over 19,000 animals. Approximately300 malignant neoplasms were recognized in the mammals andbirds of this series, and of these 23, or about 7 %, were primaryepithelial tumors of the lungs. Lung cancers were not discoveredin reptiles and amphibians.

Pulmonary cancers were found in 7 families of mammals and4 families of birds as follows : in mammals 4 squamous cell carcinomas and 5 adenocarcinomas, and in birds 13 adenocarcinomasand 1 undifferentiated carcinoma.

Aside from its occurrence in the family Anatidae, primarylung cancer would be considered a rare tumor in the collectionof the Philadelphia Zoo. Ten pulmonary adenocarcinomasoccurred among ducks and geese between 1943 and 1961. Averagelongevity of anatids on exhibition had not changed significantlyduring the period from 1901 to 1964; thus increased frequencyof lung cancers could not be attributed to advanced age of theducks and geese on exhibition. Rather, attention was focusedon the possibility of increasing amounts of carcinogens in theatmosphere because ducks and geese were kept outdoors theyear around.

Introduction

Postmortem examinations at the Philadelphia ZoologicalGarden have been continuous since 1901 and by December 31,1964, included records on over 19,000 animals. Approximately30% of this series have been mammals, 60% birds, and 10%

reptiles and amphibians. These animals have represented upwards of 50 orders and 200 families with correspondingly greaternumbers of genera and species.

Approximately 300 malignant neoplasms had been recognizedin the mammals and birds of this series by December 31, 1964,and of these 23, or about 7 C/@were primary epithelial tumorsof the lungs. Current concern with lung cancer in man suggeststhat a description of lung cancer in mammals and birds thathave shared the urban environment may warrant interest atthis time. Accordingly, we will consider the frequency of lungcancer in these animals in relation to age, sex, species, and other

1 Supported in part by Grant HE-04759 from the USPHS. We

are indebted to Dr. H. L. Stewart, National Cancer Institute, forreviewing this material.

514 CANCER RESEARCH VOL. 26

Primary Lung Cancers in Birds and Mammals of thePhiladelphia Zoo'

ROBERTL SNYDERAND HERBERTL RATCLIFFEPenrose Research Laboratory, Zoological Society of Philadelphia and the Department of Pathology, University ofPennsylvania, Philadelphia,

Pennsylvania

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Lung Cancers in Birds and Mammals

distinguished from simple squamous metaplasia by local infiltration with or without metastasis. Undifferentiated carcinomaswere tumors that formed solid masses of cells with few if anyacinar structures. These cells were anaplastic and did not suggest the appearance of bronchial epithelium.

The tumors listed in Table 1 include examples from the reviewof 1933 (3), when all specimens to that date were reexaminedand doubtful ones, chiefly squamous metaplasia, omitted. Wehad available for this review microscopic slides from 5 of the 7examples of lung cancer listed in the 1933 report. These 7 examples of lung cancer are 3 squamous cell carcinomas, 2 adenocarcinomas, and 2 pleural endotheliomas. The last 2 named werefrom a Cape hunting dog and a clouded leopard. They weretermed pleural endotheliomas when 1st examined in 1912 and1929, but we prefer to regard them as carcinomas of the lung

and not primary in the pleura. Sections of the tumor of the Capehunting dog show adenocarcinoma which suggests the possibiity of a hidden primary growth in the lung. The leopard had

advanced pulmonary tuberculosis which might have obscured ordestroyed a deeply located primary tumor. The term pleuralendothelioma reflects a period in history when rigid classifications were attempted. This does not imply that mesothelioma isan improper term, but that these tumors in all probability didnot develop from the pleura.

The earlier examples of squamous cell carcinomas might haverepresented squamous metaplasia. However on review the caseslisted here were considered to be malignant because tumor cellsinfiltrated locally. Also the tumor in the Malayan civet, althoughpredominantly of the squamous type, contained elements ofadenocarcinoma. A major bronchus was greatly dilated and the

TABLE 1

COMMON NAME, SCIENTIFIC NAME, SEX, EXHIBITION PERIOD IN

MoN@rais(IN PARENTHESES), YEAR OF DEATH, ANDTYPE ANDBEHAVIOR OF TUMORS OF AFFECTED ANIMALS

MAMMALS

CanidaeaCape Hunting dog (Lycaon pictus) 9 (4) 1929 . . . Pleural

endotheliomaRed wolf (Canis niger) 9 (177) 1962 . . . Adenocarcinoma,

metastasis to a kidneyFelidae

Clouded leopard (Felis nebnlosa) ci―(127) 1912 . . . Pleuralendothelioma

Mustelidae―Striped skunk (Mephitis mephitis) @? (71) 1955 . . . Adeno

carcinomaNorth American otter (Lutra canadensis) d' (185) 1962 . .

Squamous cell carcinoma, spread to mediastinum and heartViverridae

Malayan civet (Viverra tangalunga) d' (2) 1906 . . . Squamouscell carcinoma

DidelphiidaeCommon opossum (Didelphis marsupialis) 9 (7) 1930 . .

Squamous cell carcinomaPeramelidae

Rabbit-eared bandicoot (Thylacomys lagotis) a―(68) 1918 . .Squamous cell carcinoma

Capromyidae―— Coypu (Myocastor coypu d (41 1924... Adenocarcinoma

TABLE 1—Continued

BIRDS

AnatidaeaRed-billed tree duck (Dendrocygna autumnalis) 9 (96) 1943 . .

Adenocarcinoma, spread to abdominal air sacs and adrenalsand metastasis to liver

Shoveler duck (Spatula clypeata) 9 (72) 1953 . . . Adenocarcinoma, spread to pericardium, esophagus, and air sacs, andmetastasistoliver

Shoveler duck (Spatula clypeata) a―(31) 1954 . . . Adenocarcinoma, primary in left lung. Metastasis to syrinx, air sacs.pectoral muscles, and right lung

Cinnamon teal (Anas cyanoptera) 9 (72) 1955 . . . Adenocarcinoma, metastasis to heart, aorta, liver, and muscles

Redhead duck (Nyroca americana) 9 (130) 1957 . . . Adeno.carcinoma, spread to thoracic air sacs

Redhead duck (Nyroca americana) 9 (52) 1957 . . . Adeno.carcinoma

Upland goose (Chloephaga leucoptera) a―(9) 1957 . . . Adeno.carcinoma, spread to thoracic and abdominal air sacs

Shoveler duck (Spatula clypeata) a―(129) 1957 . . . Adenocarcinoma, spread to right thoracic air sac

Chiloe widgeon (Mareca sibilatrix) d―(12 days) 1961 . . . Adenocarcinoma, spread to thoracic and abdominal air sacs, andmetastasis to an adrenal

Redhead duck (Nyroca americana) 9 (121) 1961 . . . Adeno.carcinoma, spread to thoracic air sacs

PhasianidaeaSilver pheasant (Gennaeus nycthemerus) o@ (107) 1927 . .

AdenocarcinomaRed-jungle fowl (Gallus gallus) 9 (160) 1947 . . . Adenocar

cinomaCathartidaea

Africaii eared vulture (Torgos tracheliotus) 9 (276) 1951 . .Adenocarcinoma

PloceidaeJava sparrow (Padda oryzivora) 9 (5) 1942 . . . Undifferentiated

carcinoma, spread to air sacs

a Caged outdoors for the major part of the exhibition period.

peribronchial spaces packed with squamous cells. The adenocarcinomatous structures might have represented greatly hypertrophied and distorted bronchial glands. These tumors did notmetastasize.

The 2 adenocarcinomas seem to have been truly malignant asthey involved large portions of both lungs.

Since 1934, 2 adenocarcinomas and 1 squamous cell carcinomawere recorded in mammals. The adenocarcinoma in the redwolf metastasized to a kidney. Structural elements of this tumorare illustrated in Fig. 1. The adenocarcinoma in the stripedskunk is illustrated in Figs. 2 and 3. These 2 tumors were notalike. In Fig. 1 the structures are acini although not well differentiated and cells are columnar. The acinar structures in theskunk might be termed alveologenic since they bear a resemblance to alveoli of the lungs and the cells are cuboidal (Fig. 3).

The squamous cell carcinoma in the otter spread to the mcdiastinum and covered a portion of the visceral pericardium (Figs.4-6).

Ten pulmonary cancers occurred among the anatids between1943 and 1961. Characteristically these cancers involved large

portions of both lungs and spread over the surfaces of the air

515MARCH 1966

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FAMILY1901—19341935—1964No.ex

hibited%exhibited12 mo orlongerNo.

withlung

cancerNo.

cxhibited%

exhibited12 mo orlongerNo.

withlung

cancerMammals

CanidaeFelidaeMustelidaeViverridaeI)idelphiidaePeramelidaeCapromyidaeTotals

BirdsAnatidaePhasianidaeCathartidaePloceidaeTotals201

19012860

2486

15848

560480

45931201656

534873

4178740

59586755571

1011116

01

001125

11271252502

360

1127411

21259181869

70839240

071

7776

9173761

0200

03

101

11

13

NUMBERSLi@z

QUARTERSI

II IIIIV1901—1934

1935—1964330 8690.610.30 0.07 0.02

0.66 0.28 0.04 0.02

Robert L. Snyder and Herbert L. Rateliffe

TABLE 2

PRIMARY LUNG CANCERS IN MAMMALS AND BIRDS

TABLE 3

PROPORTION OF ANATIDS THAT DIED DURING EACH QUARTER OF A

POTENTIAL MAXIMUM EXHIBITION PERIOD

OF 320 MoNnis

This table excludes birds that died before 12 months on exhibition.

Aside from its occurrence in the Anatidae primary lung cancerwould be considered a rare tumor in the collection of the Philadelphia Zoo. Frequency among the 7 families of mammals listedin Table 2 was 0.7075% during the period from 1901 to 1934and 0.8333% during the period from 1935 to 1964. Only 1 lungcancer was recorded in birds before 1943. The frequency of lungcancer among the 4 families of birds listed was 0.7150% for theperiod from 1935 to 1964.

The increasing liability to cancer with advanced age is welldocumented so consideration of age of the anatids is of primeimportance. Table 2 illustrates a significant improvement in12-month survival of ducks, geese, and swans after 1934 from57 to 77 %. The mean exhibition period for anatids that survivedthe initial 12-month period was 84 months for the 1st periodand 74 for the 2nd. Patterns of life-spans in the 2 periods arecompared in Table 3 (x2 = 5.79, P = 0.10). Comparison of lifespans in the 2 periods indicates that occurrence of lung cancersin these birds was not associated with increased age at death.

The significance of the increased frequency of lung cancer inbirds and in the family Anatidae particularly was tested in a2 x 2 contingency table according to the method of Fisher and

Yates (1). The increase in cancer from 1 case to 13 is significantat the 1% level; however, most of the cancers occurred amonganatids and when this family is excluded the increased frequencyis not significant. Anatids treated alone show a statisticallysignificant increase in lung cancer (P < 0.05).

Discussion

Cancers have not been uncommon in the collection of thePhiladelphia Zoo (2—4).In general the incidence of cancer inmammals has been highest in the families Canidae, Felidae,Mustelidae, Ursidae, and Viverridae and lowest in the familiesProcyonidae, Bovidae, Cervidae, Cercopithecidae, and Cebidae.Also, the incidence has been much lower in all families of birdsas compared with mammals. These differences cannot be accounted for by differences in longevity alone (4). Thus, theunexpectedly large number of cancers that occurred amonganatids between 1943 and 1961 is worth consideration.

Lombard and Witte (2) have already suggested air pollutionas a possible causative factor for cancers among the waterfowlin the zoo. The ducks, geese, and swans were kept outdoorsthe year around on a large lake and a series of connecting poolsor ponds. The pheasants were kept outdoors in wire enclosures.Other birds were caged indoors continuously or were moved

sacs. I'@Ietastases involved the liver 3 times, muscles twice, andthe syrinx, the heart, the aorta, and the adrenals once. Thecancer cells tended to extend along the surfaces of the air sacsin continuous sheets, but in a few instances isolated nodules inthe air sacs suggested that cancer cells were transported to thesesites in the blood stream or in the fluid exudate sometimes foundin the air sacs. Most of these tumors consisted of acini containing mucinous secretions (Fig. 7). Typical structures consisted of

well-differentiated columnar cells like those illustrated in Fig. 8.Pulmonary cancers of the anatids were all termed adenocarcinomas.

Three adenocarcinomas and 1 undifferentiated carcinomawere found in the families Phasianidae, Cathartidae, and Ploceidae. Essentially the adenocarcinomas resembled those foundamong the anatids ; however, air sacs were not invaded andmetastases were not found. The histologic appearance of thetumor from the African eared vulture is illustrated in Fig. 9.The tumor in the Java sparrow of the family Ploceidae consistedof solid sheets of cells which did not form acini. Nuclei wereround, hyperchromatic, and the cytoplasm was clear.

FREQUENCY OF LUNG CANCERS. Table 2 summarizes data per

taining to frequency of occurrence of lung cancers in mammalsand birds between 1901 and 1964. The table is divided into 2periods, 1901—1934and 1935—1964.New and improved standardized diets instituted in 1933 and 1934 brought about a significant increase in survival time for most families of mammalsand birds. A detailed statistical treatment of life-spans in thezoo as related to frequency of cancer was published earlier (4).In that paper average exhibition periods were listed for 9 familiesof mammals and 5 families of birds, but the data included onlyanimals that had lived in the collection for at least 12 monthsto emphasize the high mortality common to newborn animalsand recent arrivals. Data in Table 2 were derived from all animals, regardless of age, and show a significant improvement insurvival of young animals after 1934.

516 CANCER RESEARCH VOL. 26

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Lung Cancers in Birds and Mammals

outdoors for the summer months. If airborne carcinogens wereinvolved, one must assume that concentrations were lowerindoors. In this respect mammals that have developed lungcancers as a rule have spent the major part of their life in thezoo in outdoor enclosures. For example, the otter spent 15years in an outdoor pool and the dogs had outdoor runs andsmall sheltered dens. The bandicoot and the civet would be theexceptions to the general rule. The civet, of course, was onlyin the collection for 2 months, so might have had lung canceron arrival. Two of the ducks fall into this category too, 12 daysand 9 months on exhibition, which only proves that lung cancersin these birds are not limited to this zoo population.

The role of species susceptibility to lung cancers should alsobe discussed briefly. Primates have been free of lung cancerseven though longevity has increased. The average exhibitionperiod of adapted (12-month survival) members of the familyCercopithecidae for the period 1935—1962was 96 months. However, one might argue that these were still comparatively younganimals at death. These animals are caged indoors except duringthe summer months. The families Cervidae and Bovidae havebeen well represented in the collection and are caged outdoorsthe year around. Exhibition periods have been reasonably long,yet lung cancers have not been encountered. Mean exhibitionperiods of 77 bears, which were also caged outdoors, were 100months during the period before 1935 and 206 months after1935.

From a statistical viewpoint one can argue (from Table 2)that only 1 or 2 cases have occurred in any 1 family over aperiod covering 64 years ; the exception, of course, is the familyAnatidae. The occurrence of a single lung cancer in the nextfew years in a family hitherto free of this disease would not beunexpected. Thus, there is no reason to conclude that certainfamilies of mammals might be resistant to lung cancer.

Within the family Anatidae is an apparent predilection forlung cancer among 2 species, the shoveler duck and the redheadduck, for the 2 species combined accounted for 6 of the 10 casesof lung cancer. Such an occurrence suggests a familial relationship, identical sites of capture, or a peculiar feeding habit forthese species.

We conclude from this review that lung cancers are comparatively rare tumors of captive birds and mammals, but in viewof the occurrence of pulmonary cancers among birds and mam

mals caged outdoors more attention should be focused on therole of airborne carcinogens. Particles settling out of the air maybe concentrated in the water or on the soil, in which case a roofmight provide some protection for the animals inside. Apparentspecies susceptibility in the shoveler and redhead ducks mightbe a matter of behavior that places these birds in close contactwith the carcinogen.

These conclusions, of course, are only valid if the primarydata are reasonably correct. We cannot say as eye witnesseshow complete or how carefully each necropsy was done from1901 to 1964. It has been the practice of this laboratory to publish an annual report in which patterns of disease are discussedin some detail. We judged from reading the protocols and theannual reports that errors of selection of cases due to unreliablepostmortem work must be scattered at random over the entire64-year period. The preponderance of lung cancers in anatidsfrom 1943 to 1961 is the only significant departure from thenorm and cannot be accounted for by reason of longer life-spans.It seems highly unlikely that lung cancers were not recognized

in anatids prior to 1943, because necropsy procedures have always been the same. Lung tissue was not examined microscopically in every instance, but detection of tumor nodules mustdepend initially on careful gross examination of the lungs. Thusin the last analysis the degree of error of cancer frequency statistics depends on the completeness of the gross examination.In this respect there is no reason to believe that the statisticspresented in this report are grossly in error.

References

1. Fisher, R. A., and Yates, F. Statistical Tables for Biological,Agricultural, and Medical Research, Ed. 4. Edinburgh andLondon: Oliver and Boyd, 1953.

2. Lombard, L. S., and Witte, E. J. Frequency and Types of Tumors iii Mammals and Birds of the Philadelphia ZoologicalGarden. Cancer Res., 9: 127—41,1959.

3. Ratcliffe, H. L. Incidence and Nature of Tumors in CaptiveWild Mammals and Birds. Am. J. Cancer, 17(1): 116—35,1933.

4. Snyder, R. L., and Ratcliffe, H. L. Factors in the Frequencyand Types of Cancer in Mammals and Birds at the PhiladelphiaZoo. Ann. N. Y. Acad. Sci., 108: 793—804,1963.

5. Willis, R. A. Pathology of Tumors, Ed. 3. Washington : Butterworths, 1960.

FIG. 1. Adenocarcinoma, red wolf 9 on exhibition 177 months. X 100.

FIG. 2. Adenocarcinoma, striped skunk@ on exhibition 71 months. X 100.

FIG. 3. Higher magnification of tumor illustrated in Fig. 2. The cells are cuboidal and acini resemble aveoli. X 560.FIG. 4. Portions of the lungs and mediastinum from North American otter a―on exhibition 185 months. Tumor was squamous

cell carcinoma.FIG. 5. Microscopic appearance of tumor illustrated in Fig. 4. Nests of tumor cells are found within the wall of a major bronchus,

between a cartilaginous ring and the lumen. X 100.FIG. 6. Higher magnification of squamous cell carcinoma in the otter's lungs. Tumor cells scattered in connective tissue stroma.

x 560.FIG. 7. Adenocarcinoma, Chiloe widgeon ci@ on exhibition 12 days. Cells are arranged in acini with abundant mucinous secre

tions. X 100.FIG. 8. Adenocarcinoma, redhead duck 9 on exhibition 121 months. Structures consist of relatively well-differentiated tall

columnar cells with basal nuclei. X 560.FIG. 9. Adenocarcinoma, African eared vulture 9 on exhibition 276 months. Tumor consists of large glandular structures with

abundant stroma. Black spots are deposits of coal pigment. X 100.

517MARCH 1966

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Robert L. Snyder and Herbert L. Ratcliffe

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1966;26:514-518. Cancer Res   Robert L. Snyder and Herbert L. Ratcliffe  Philadelphia ZooPrimary Lung Cancers in Birds and Mammals of the

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