Zierenberg-Ripoll, Alexandra

1

The Effects of Second-hand Smoke on Canine Lung Tumors

Abstract

Second-hand cigarette smoke is a recognized carcinogen, which has been shown to correlate with

the development of pulmonary neoplasia in people. Dogs with spontaneous pulmonary cancer

represent an interesting and unique population as they are exposed to similar environmental

factors as the people with whom they live with. Thus, we propose that evaluation of dogs with

primary lung tumors, especially those with documented exposure to chronic second-hand smoke

from owners, would assist in determining the actual impact of second-hand smoke on the

development of lung cancer. A survey study was developed and distributed to the owners of dogs

in three target groups; a group with confirmed primary lung tumors (affected group), a group

with cutaneous mast cell tumors (control group 1), and a group with neurologic dysfunction and

no evidence of cancer (control group 2). Additionally, the radiographic features of lung tumors in

dogs with and without documented tobacco smoke exposure will be compared to assess for

features unique to smoke exposure. Preliminary results indicate that smoking occurred in 13%

(10/79) of the households where dogs were diagnosed with primary lung tumors, 16% (9/55) of

the households where dogs were diagnosed with mast cell tumors, and 6% (2/33) of the

households where dogs needed neurologic evaluation. Data acquisition is ongoing.

Goals

The goals of this study are to 1) determine if exposure to tobacco smoke correlates with the

development of primary pulmonary neoplasia in dogs and 2) characterize imaging features of the

different types of primary lung tumors in dogs. We hypothesize that dogs exposed to cigarette

smoke will have a higher incidence of pulmonary neoplasia and that the radiographic appearance

of smoke induced tumors will be unique to other types of primary lung tumors.

Materials and Methods

Study Evaluation: Prior to commencing the proposed objective, a power statistical analysis was

performed to determine the approximate number of dogs needed in the affected group and the

number of dogs needed in the control groups. A two-group continuity corrected χ2 test of equal

proportions (odds ratio=1) (unequal n’s). Assuming that 15% of responders were smokers, 374

lung cancer dogs would be needed with 747 control group dogs. The 747 control dogs were

divided into the mast cell tumor group and the neurologic dysfunction with no other neoplasms

group.

Patient Selection: To reach the proposed objective, a search was performed within the database

of the Veterinary Medicine Teaching Hospital at the University of California, Davis from

January 2002 to May 2012. For inclusion in the primary lung tumor group, dogs must have had a

cellular diagnosis of pulmonary carcinoma, adenocarcinoma, histiocytic sarcoma, or squamous

cell carcinoma. Confirmation of disease was by biopsy, cytology, or necropsy. Two control

groups were selected for comparison. Control group 1 included dogs with a histologic or

cytologic diagnosis of cutaneous mast cell tumor and with no other neoplasms. Control group 2

consisted of dogs with neurologic dysfunction and with no other neoplasms.

Zierenberg-Ripoll, Alexandra

2

Survey Development: A survey was developed and distributed by mail. Main survey topics

included patient history, diet, exposure to flea medications, housing description, exposure to

second-hand smoke and other inhaled products such as fertilizers and aerosols. Dog owners were

instructed to answer questions about environmental exposure as they pertained to the last 5 years

of the animals’ life prior to diagnosis. This survey also intended to quantify the amount of

exposure to environmental toxins including tobacco. All three groups were given the same

survey to complete.

Imaging Assessment: When available, thoracic radiographs were reviewed for imaging features

including type of pulmonary pattern as well as lesion size, number, location, margination, and

distribution. The presence of lesion mineralization or cavitation, hilar lymph node enlargement

and pleural effusion was recorded.

Results

Surveys were sent to owners of dogs with confirmed diagnosis of a primary lung cancer (affected

group-284 cases), owners of dogs having a mast cell tumor (control group 1-260 cases), and

owners of dogs requiring neurologic evaluation and with no evidence of cancer (control group 2-

263 cases). A total of 718 surveys were mailed. To date, 23% (167) surveys have been

successfully received and recorded with preliminary results indicating that smoking occurred in

13% (10/79) of the households where dogs were diagnosed with primary lung tumors, 16%

(9/55) of the households where dogs were diagnosed with mast cell tumors, and 6% (2/33) of the

households where dogs needed neurologic evaluation.

Surveys will continue to be analyzed as they arrive in the following weeks with the preliminary

expectation that we will have to send a second round of surveys to maximize data collection.

Thus, statistical analysis of our results will not occur until we have received and recorded as

many surveys as possible. Moreover, radiographic assessment will not occur until we know

which animals’ surveys are returned and, therefore, which images to evaluate. Should we not

receive enough surveys to adequately assess the effect of second hand tobacco smoke on the

development of lung cancer in dogs, we intend to recruit additional cases from another veterinary

teaching institution.

Summary

In order to investigate tobacco smoke as an environmental toxin and to assess its’ detrimental

health effects on dogs, we proposed to evaluate the home environment of owners with dogs

diagnosed with primary lung cancer. This was assessed with the development of a survey that

was distributed to 3 target groups (primary lung tumor, comparison group 1-mast cell tumor, and

comparison group 2- neurologic consultation). Due to the preliminary stages of the study, final

statistical results are still being processed as surveys are received.