A case-control study was conducted in China to investigate the association between cellular phone use and epithelial parotid gland malignancy.
Regular exposure was defined as at least one call per week for 6 months or more before the time of diagnosis.
| Group | Description |
|---|---|
| Reference group 1 | frequency of use: never or rarely |
| Group 2 | frequency of use: regular use |
| Reference group 3 | duration since first use to the time of diagnosis: never or rarely |
| Group 4 | duration since first use to the time of diagnosis: 0.5 - 6 years |
| Group 5 | duration since first use to the time of diagnosis: 7 - 8 years |
| Group 6 | duration since first use to the time of diagnosis: 9 - 10 years |
| Group 7 | duration since first use to the time of diagnosis: > 10 years |
| Reference group 8 | calculated duration of cellular phone use: never or rarely |
| Group 9 | calculated duration of cellular phone use: 0.5 - 6 years |
| Group 10 | calculated duration of cellular phone use: 7 - 8 years |
| Group 11 | calculated duration of cellular phone use: 9 - 10 years |
| Group 12 | calculated duration of cellular phone use: > 10 years |
| Reference group 13 | average daily use: never or rarely |
| Group 14 | average daily use: ≤ 0.5 hours |
| Group 15 | average daily use: 0.5 - 2.5 hours |
| Group 16 | average daily use: > 2.5 hours |
| Reference group 17 | average daily longest time of a single call: never or rarely |
| Group 18 | average daily longest time of a single call: ≤ 0.5 hours |
| Group 19 | average daily longest time of a single call: 0.5 - 2.5 hours |
| Group 20 | average daily longest time of a single call: > 2.5 hours |
| Reference group 21 | average daily number of calls: never or rarely |
| Group 22 | average daily number of calls: ≤ 8 |
| Group 23 | average daily number of calls: 9 - 10 |
| Group 24 | average daily number of calls: > 10 |
| Reference group 25 | number of calls since first use: never or rarely |
| Group 26 | number of calls since first use: ≤ 24,000 |
| Group 27 | number of calls since first use: 24,001 - 42,000 |
| Group 28 | number of calls since first use: > 42,000 |
| Reference group 29 | time of calls since first use: never or rarely |
| Group 30 | time of calls since first use: ≤ 1350 hours |
| Group 31 | time of calls since first use: 1351 - 4320 hours |
| Group 32 | time of calls since first use: > 4320 hours |
| Reference group 33 | preferred side of calling: never or rarely |
| Group 34 | preferred side of calling: ipsilateral |
| Group 35 | preferred side of calling: contralateral |
| Group 36 | preferred side of calling: ipsilateral and contralateral |
| Cases | Controls | |
|---|---|---|
| Eligible | 221 | 2,643 |
| Participants | 136 | 2,051 |
| Participation rate | 62 % | 78 % |
Overall (between reference group 1 and group 2), frequency of cellular phone use was not significantly associated with parotid gland malignancy . However, statistically significant associations were observed in subgroups of the univariate analysis (e.g., duration since first use > 10 years, average daily use > 2.5 hours, calculated duration of use > 10 years) and in subgroups of the multivariate analysis (e.g., number of calls since first use > 42,000 (OR 15.4, CI 13.3-17.4), calculated duration of use 9-10 years (OR 7.7, CI 6.2-9.2), average daily use > 2.5 hours (OR 6.0, CI 1.5-24.5).
Female gender, advanced age, married status, higher education, higher monthly income, and smoking were associated with increased risk of epithelial parotid gland malignancy, especially mucoepidermoid carcinoma.
No statistically significant association between ipsilateral cellular phone use and epithelial parotid gland malignancies was found which indicates that a definitve conclusion about cellular phone use and parotid gland malignancy cannot be made.
The authors conclude that the results suggest a possible dose-response relationship of cellular phone use with epithelial parotid gland malignancy. They suggest that the association of cellular phone use and epithelial parotid gland malignancy requires further investigation with large prospective studies to reduce bias and confirm the results.
Selection bias and recall bias cannot be excluded. Regular use was defined as at least one call per week for 6 months or more prior diagnosis, whereas epithelial parotid gland malignancies are not likely to be induced by such a short exposure time, so this might have led to misclassification bias.
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