The phrase "a pet topic of" is correct and usable in written English.
It can be used to refer to a subject that someone is particularly fond of discussing or has a strong interest in.
Example: "Climate change has become a pet topic of many activists who are passionate about environmental issues."
Alternatives: "a favorite subject of" or "a preferred topic of".
Long a pet topic of Bill Joy, Sun's co-founder and chief scientist, a host of distributed computing initiatives is being pursued within the company.
But in recent decades, rising unemployment, poor housing problems and the questioning of the presence of Islam in a secular state have made immigration a pet topic of the far-right.
Space exploration and travel have been a pet topic of interest for tech moguls, including Elon Musk — the founder of PayPal — whose private spaceship was recently cleared for launch to the International Space Station.
Immunology is somewhat of a pet topic for Parker.
An officer in one of the 38th's infantry battalions, who met Cubitt in early June, shortly after he took command, described him as "a very large and fierce-looking major-general, with two rows of ribbons, and a gleam in his eye", who proceeded to interrogate a subaltern about the exact type and position of his unit's trench latrines, apparently something of a pet topic.
The ratings, Miles said, give him valuable tips about his own future instructors and have prompted at least one teacher at his school to "scale back a bit" on her tiresome discussions of a pet topic.
What next?" It's just a pet favourite topic of mine, Paul.
For my family, they were exceptionally good pets and a favorite topic of conversation.
Dr Megan Poe has been obsessed with the subject of love since childhood – and now her pet topic is blossoming into a mini-phenomenon.
Since its release he's drawn praise from everyone from Elton John to Noam Chomsky; and later this year he'll cover his pet topic with Naomi Klein at the Festival of Dangerous Ideas in Sydney.
Four minutes into his 20-minute address to a crowd of more than 1,000 festivalgoers, the former prime minister had broached one of his pet topics, calling for an overhaul of the Westminister system and the abolition of the states.
