Complex sentence: Such disturbances of the vestibular system could also be cancer related, such as cerebral or vestibular secondaries (metastasis) or cancer treatment related such as the use of opioids or radiation therapy of the head and neck which may affect the system.
Split into simpler sentences: Such disturbances of the vestibular system could also be cancer related, such as cerebral or vestibular secondaries (metastasis). They could also be cancer treatment related such as the use of opioids or radiation therapy of the head and neck which may affect the system.