Is second hand vaping harmful? i've had breast cancer and am concerned about being around them when they vape.

Yes: The aerosol that is exhaled by a person "vaping" or using e-cigarettes does indeed carry chemicals that can be harmful to a person exposed to these vapors. See https://no-smoke.org/electronic-smoking-devices-secondhand-aerosol/

Secondhand aerosol : from ESDs contains nicotine, ultrafine particles & low levels of toxins that may cause cancer. (Acetaldehyde (MS), Benzene (SS), Cadmium (MS), Formaldehyde (MS,SS), Isoprene (SS), Lead (MS), Nickel (MS), Nicotine (MS, SS), N- Nitrosonornicotine (MS, SS), Toluene (MS, SS).) REF: https://no-smoke.org/electronic-smoking-devices-secondhand-aerosol/