"unwelcome topic" is correct and usable in written English.
You can use it when you want to refer to something which is not pleasant or comfortable to talk about. For example: "The war in Syria is an unwelcome topic among many people."
Foreign academics have also been targeted, with Chinese authorities denying visas to academics deemed to be focusing on unwelcome topics.
These rhetorics elide and confound environmental toxicity, a discourse that tends push the unwelcome topics of prevention, fatality, and collective risk to the fore.In addition to photos of smiling women and children, NBCAM.org's homepage states, "Today, we remain dedicated to educating and empowering women to take charge of their own breast health" (NBCAM).
But during his three-day stay, Major made no bones about raising unwelcome political topics, publicly challenging Beijing over religious freedom, freedom of speech, an uprising in Tibet, the detention of student demonstrators and the massacre.
I also noticed the topic was an unwelcome one among family members and friends.
Graham's turn does not appear to be designed to convey sympathy, despite this being a troubles telling, and again there are signs that the topic may be unwelcome.
Writing in other than e-mail or text message shorthand is an unwelcome burden for many students, and researching topics beyond Wikipedia snippets is a rare chore in which few indulge.
Some lawyers and political analysts say the case could prove embarrassing to the mayor, in shining an unwelcome spotlight on one of his least favorite topics: how he spends his own money.
The economic slump and nationalist backlash in Europe have made immigration a hot political topic, so low-skilled migrants are often unwelcome.
People bombarded with unwelcome salary information, or pressed to disclose it, assume someone is raising the topic to subtly brag, or put someone else down, he said.
Topics like sex and dating, par for the course in most comedy clubs, but unwelcome to many religious Muslims, are raised there, often to audiences including women, laughing heartedly under traditional veils.
