Tanya has only confided in daughter Lauren (Jacqueline Jossa) over her illness, preferring to keep it a secret from the rest of her family. She also recently made the shock decision to stop having treatment.
Speaking on Loose Women today, Joyner explained: "She's kind of dealing with it in a way that I think I would never deal with it, but who knows what we would react like? And it will come out over the next couple of days, exactly why she has got such a deep-seated fear about it all, and what her connections are with it.
"You're reading the scripts thinking, 'Poor Lauren', but then you've got to justify it because you've got to go and do it."
She continued: "You can only really tell one person's story. There's always going to be some people who will go, 'When I had chemo, I never did that'. But I do take it very seriously. I looked at the particular treatment for this particular cancer, because they're all very different and they all affect you in very different ways."
Joyner said that the general response to Tanya's story has been "positive", adding that she is looking forward to the new twists in store now that Max (Jake Wood) is back on Albert Square.
She said: "We'll wait and see. Will she have him back? Will she want him back? Will he want her? It's a very different situation now."
EastEnders continues tonight at 7.30pm on BBC One.
> EastEnders' Tanya, Max relationship divides fans, says Jo Joyner
> EastEnders star Jake Wood chats to Digital Spy
> Read more EastEnders spoilers and news