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Lemen et al. (1976) conducted a retrospective cohort study of cancer incidence in a group of 115
white male anion-exchange resin manufacturing workers in San Mateo County, California. Worker
tobacco smoking status was evaluated and used to adjust expected tumor incidence rates. Five cases
of lung cancer were observed compared to 0.54 cases expected (p < 0.01), representing a nine-fold
increased lung cancer risk. The histological type of lung cancer primarily observed was small cellundifferentiated;
exposure ranged from 7.6 to 14 years (mean of 10 years). The mean induction-latency
period was 15 years. No quantitative worker exposure evaluation was performed.
The studies described above demonstrated a significant increase in lung cancer incidence, predominantly
small-cell-undifferentiated carcinoma. This histologic type is not the one generally associated with
smoking (squamous cell carcinoma).
Animal Studies
Male Sprague-Dawley rats and golden Syrian hamsters (50/exposure group) received 1, 3, 10 or 30
exposures (6 hours/exposure) to 1 ppm BCME by inhalation (Drew et al., 1975). After exposure, the
animals were exposed for the remainder of their lifetime. Median survival time for hamsters receiving 0,
1, 3, 10 or 30 exposures was 675, 620, 471, 137 and 42 days, respectively. Median survival time for
exposed rats was 467, 457, 168, 21 and 23 days, respectively. One rat in the 3 exposure group
developed a squamous-cell carcinoma of the skin; additionally, one hamster in the 1 exposure group
developed an undifferentiated nasal tumor. These tumor incidences were not statistically significant.
However, the study treatment durations were short, and survival of the treated animals was poor.
Kuschner et al. (1975) exposed male Sprague-Dawley rats and golden Syrian hamsters to BCME by
inhalation. Groups of 100 hamsters and 70 rats were exposed to 0.1 ppm BCME 6 hours/day, 5
days/week. Control group sizes were not stated. Exposure was generally for the life of the animals.
After 80 exposures, 57/70 rats were still alive; 20 rats were then removed from the exposure schedule
and observed for the remaining life of the animals. Mortality at 60 weeks was approximately 90% for
rats (both animals exposed for their entire lifetime and animals receiving 80 exposures) and hamsters;
corresponding control mortality at 60 weeks was approximately 40% and 15% for rats and hamsters,
respectively. Two rats in the group receiving 80 exposures developed tumors; the tumor types were a
nasal esthesioneuroepitheloma and a keratinizing squamous cell carcinoma of the lung. Additionally, one
hamster developed an undifferentiated carcinoma of the lung. No corresponding tumors were reported
in control rats or hamsters. Additional groups of rats were given 0, 10, 20, 40, 60, 80 or 100 6-hour
exposures to 0.1 ppm BCME (group sizes 240, 50, 50, 20, 20, 30, and 30, respectively), then
observed for the life of the animals. Mortality of the exposed animals in all exposure groups was
equivalent to that of controls. Nasal and lung tumors were noted in the exposed animals. Nasal tumor
types included esthesioneuroepithelomas, unclassified malignant olfactory tumors, squamous cell
carcinomas involving the turbinates and gingiva, poorly differentiated epithelial tumors and
adenocarcinomas of the nasal cavity. Lung tumors included squamous cell carcinomas and
adenocarcinomas. Tumor incidence data for combined respiratory tract tumors is listed in Table 1.
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