Are you kidding me?
Dear Readers, here is an ADA quiz. I’m not sure you’ll be able to handle it. It’s really, really hard.

Your employee discloses that she has ovarian cancer that has metastasized to her liver. She says she will have to undergo treatment, including medication, and expects to have increased difficulty engaging in certain activities.
Here comes the hard part: Assuming that what your employee has told you is true, does she have a disability that is protected by the Americans with Disabilities Act?
YOU: “Of course she does, you silly goose!”
ME: "You are right, as always. Please forgive me for ever having doubted you."
Jo the paralegal
True story. Our plaintiff – we’ll call her Jo – was a senior paralegal for a law firm. Reading between the lines of the court documents (available here, here, here, and here), my guess is that she may have been a squeaky wheel. Maybe a little more trouble than she was worth. On the other hand, it sounds like she did a good job. She got promoted, and she says that in 2023 she got mad and quit, but the firm’s Chief Operating Officer talked her into coming back.
Which brings us to March 13, 2024. That day, Jo disclosed to the COO and the owner of the law firm that ovarian cancer had metastasized to her liver and that she would experience some limitations as a result. She said that she would like to continue working “as long as I can.” She also attached a note from her health care provider, which is blacked out in the court file. My best guess is that the note said she would have to be on medication because the COO allegedly responded by asking Jo whether the meds would affect her mental abilities. (The COO’s response is also blacked out, so I am only going by what Jo and her attorney said in their court documents.)
Jo replied to the COO with a not-totally-blacked-out email (yay!) saying the only difference between that day (March 13) and the prior day (March 12) was that the firm now knew about her medical condition. It was agreed that she would return to work on March 14.
Jo returned to work on March 14, and was fired.
Again, there is a lot more to this case, and I would love to hear the law firm’s side of the story. But I'm sure we all agree that the timing of the termination looks terrible. So, perhaps in desperation, the firm’s attorneys asked the court for immediate dismissal of Jo’s lawsuit, including her ADA claim.
The three main stages of litigation
When an employer gets sued, there are generally three opportunities for a win or a loss: once near the beginning of the lawsuit, once after the parties have engaged in discovery, and, of course, at trial. (I am oversimplifying, and much more on these three stages is available here.) The earlier you try to score a “win,” the more the court is required to give your opponent the benefit of the doubt.
Jo’s law firm (or the firm's lawyers) opted to try for the earliest dismissal, which requires the court to assume that the facts alleged in Jo's lawsuit are true. The firm is saying it's entitled to dismissal because Jo's lawsuit doesn't allege that she disclosed a condition that was an ADA-protected disability.

No, I'm not.
One little problem with that. According to her lawsuit, Jo disclosed ovarian cancer that had metastasized to her liver. Based on my five minutes of internet research, that's not necessarily a death sentence, but it’s very serious and probably a disability. (The "probably" part was sarcastic.)
Welcome to 17 years ago!
The Americans with Disabilities Act was enacted in 1990, and took effect for employers with 15 or more employees in 1994.
But by the turn of the millennium, the ADA had become practically a dead letter because the courts were dismissing lawsuits on the ground that the plaintiff did not have a protected “disability.” In 1999, the U.S. Supreme Court ruled that “mitigating measures” had to be taken into account in making this determination. For example, maybe you had hypertension or depression, but you took medication that kept it under control. That medication (assuming it was effective and didn't make you sick in other ways) disqualified you from having an ADA-protected disability. In another case, decided in 2002, the Supreme Court said that the condition had to “prevent” or “severely restrict” you from performing activities that were “of central importance to most people’s daily lives.”
In the view of the courts, about the only people left with valid ADA “disabilities” were those with what I call “traditional” disabilities – severe visual impairments that could not be corrected with glasses or contacts, hearing impairments that could not be corrected with hearing aids, and mobility impairments that required the use of wheelchairs.
In response to these and similar decisions from the lower courts, Congress in 2008 passed the Americans with Disabilities Act Amendments Act, which took effect in 2009. As I wrote way back in 2010, the ADAAA significantly liberalized the definition of “disability.” Medical conditions were to be considered without regard to any good “mitigating measures” – including medications and other treatments that don't have serious side effects. For example, post-ADAAA, if you have the condition of hypertension, you have what is almost surely an ADA-protected disability even if your meds keep your blood pressure at 110/60 and you feel great. (Mitigating measures would still be relevant today in determining whether you needed or were entitled to a reasonable accommodation, but they are not relevant to whether you have a disability.)
The Equal Employment Opportunity Commission issued regulations interpreting the ADAAA and said that certain medical conditions would almost always be found to be disabilities. This presumably includes most cancers, and almost certainly any cancer that has metastasized to the liver.

"So . . . you're saying this isn't a slam dunk for us . . ."
In short, I suspect that this employer's “no-disability” argument is a loser. Lawyers, and sometimes even judges, have been known to erroneously cite pre-2009 court decisions in interpreting the ADA. (No telling how much worse this will become now that artificial intelligence is being used to conduct legal research, and to write briefs and opinions.) Those older decisions may be fine as they apply to other aspects of the ADA, but they are largely obsolete when determining whether a given medical condition is a protected disability.
It’s possible that after the law firm's motion to dismiss is denied (as I expect it will be), the parties engage in discovery, and the law firm tries to get the lawsuit dismissed at the intermediate stage (summary judgment), the court will find that the law firm did not violate the ADA. Despite the lousy timing. For example, the firm might be able to prove that the decision to terminate Jo was made for legitimate reasons before she disclosed her medical condition.
But if the law firm ultimately wins the case, I predict that it will be in spite of the fact that Jo has a disability, not because she doesn’t have a disability.