The phrase 'deviate from the topic' is correct and can be used in written English.
It means to move away or wander off from the subject that is being discussed. For example, "Although the conversation had started off discussing the importance of security, it quickly deviated from the topic and soon we were talking about the latest news."
To piggyback off the previous point, speakers often deviate from the topic and description that is proposed on the schedule.
Reviews are more opinion centered as compared to blogs and forums where the focus may deviate from the topic.
If somebody talks to you, refuse to deviate from the topic of how tragic and sadly ironic life is.
This will ensure that you have a framework in mind at all times and you do not deviate from the topic.
During Saturday's program, which ostensibly dealt with airline security, a caller apparently deviated from the topic to unleash an expletive-laced attack against Savage.
A committee of religious scholars decides the content of the Friday sermons to be preached in every mosque by the imams who are all on the state payroll and forbidden to deviate from the official topic which adheres to moderate values: respect for religious minorities including Christians and for women.
The writing doesn't deviate from the given topic.
Furthermore, the course deviates from the traditional topics covered in introductory physics, spending significantly more time on the concepts of energy and thermodynamics because these topics are central to phenomena in chemistry and biology.
If someone deviates from the subject, get them back on track by saying, "That topic is for another day". Whether you're chairing the meeting or simply a participant, listen with your mind fully engaged.
He does not deviate from the party line even on topics where a variety of positions are theologically permissible, such as the end of clerical celibacy.
