Cellphone towers do emit harmful radiation and if you're up close to the cellphone towers working on them while the cellphone tower is operating then yes you can be exposed to harmful radiation which can lead to cancer.
You really only feel the effects of the RF Radiation and will potentially get cancer if you're close enough to the cellphone towers to be working on them.
Still even your cellphone emits some RF radiation and can be harmful to your health but I wouldn't worry to much about it.