CHRONIC UPPER RESPIRATORY INFECTION
Andromeda and her brother Orion both came down with an upper respiratory infection shortly after we got them, which didn't surprise us since one of their littermates had been ill.  Orion recovered quickly, but Andromeda continued to sniffle and sneeze and periodically get a fever despite several rounds of medication.  She was about 8 weeks old when she first got sick and it wasn't until she turned almost nine months old that the symptoms finally ceased.  She wasn't miserably ill the entire time, of course: it's just that the sniffling and congestion never went away.
We delayed having Andromeda spayed since her condition made her a surgery risk, but when it was apparent she'd recovered, we scheduled her.  Naturally, she went into heat several days before the appointment and made an incredible amount of noise. 
She had several more upper respiratory infections in the second year of her life and seemed to catch them at the drop of a hat.  We think the root cause of her problems may have been a herpes virus, but we'll never know for sure.  She recovered quickly from the later infections after being put on antibiotics, which doesn't make a whole lot of sense if she had a virus.

When she had infections, Andromeda produced an amazing amount of snot, and since she was a friendly, people-oriented cat, she tended to sneeze all over us.  I'm sure she didn't understand why we screamed and ran...

Fortunately, she quit getting the infections in early adulthood.
ADENOCARCINOMA

In late May of 2009, Chris was petting Square and noticed a small lump on her neck. We took her in to have it checked out and a biopsy revealed that it was adenocarcinoma, a type of cancer. It appears to have originated in a salivary gland. The only symptom we had noticed was that she'd been snoring a bit more loudly than usual - a result of the lump taking up some space near her trachea.

The veterinary oncologist took x-rays, which showed that the cancer had quickly spread from the salivary gland to the adjacent lymph gland, then into lymph glands in her chest. Because of this, there was no possibility of a cure. We decided to treat her with palliative radiation and chemotherapy in the hopes of buying her some time - a decision we made after the vet informed us that both treatments are usually well tolerated by cats and cause few side effects.

As of this writing, she's had one radiation treatment and one chemotherapy treatment and sure enough, neither seems to have had any adverse side effects. 
October 2009 Update
The radiation treatment was much more successful than anyone anticipated: there is no longer any trace of the original salivary gland tumor. Square tolerated the chemotherapy drug, Carboplatin, very well, but x-rays revealed that it didn't shrink the tumors in her chest so she is now on a different drug. 
This second drug is called Palladia and it is relatively new. As with the Carboplatin, she doesn't have any nausea or vomiting - in fact, it seems to make her feel better than usual. She's more active than she has been in a long time and even plays with cat toys, which she hadn't really done since even before she got cancer.
The Palladia does have one side effect: it has altered her appetite. Square has never in her life been into "people food" at all, and even turns her nose up at fish when we cook it for the turtles. After starting on the Palladia, she's begun to sample all kinds of odd food, including tofu and brownies.

December 2009 Update
She continues to do very well on the Palladia. There is now a small growth at the site of the original tumor, but it's tiny and so far hasn't grown any. Since it's not causing any problems at this point, we're just monitoring it. 
She goes in for bloodwork every few weeks and x-rays every so often and has made all kinds of friends at the oncology clinic. As I write this, she is running around the living room, chasing a mouse toy. We never thought she'd do this well for this long and we're grateful for that every day. 

January 2010 Update
The growth noted in December has, unfortunately, gotten a bit larger. We can't do radiation on that site again, so at this point, we're just monitoring it and hoping it grows very, very slowly.

March 2010 Update
The original growth continues to grow slowly. In addition, there is a new, very small growth under her chin and she has a swollen lymph gland in her neck, which is an indication that the cancer is spreading. 
Her oncologist advised us to discontinue the Palladia, since it's no longer doing any good. We've opted to put her on prednisolone, which will help reduce any inflammation and make her feel good for the remainder of the time she has. At this time, she appears to feel just fine and is eating well, maintaining her weight, pursuing her usual activities, and enjoying life. 

May 18, 2010 Update
She'd slowed down some over the past few weeks, but was still eating quite heartily, going about her usual business, and enjoying catnip. On May 17th, however, she started looking more tired than usual and seemed weak. On the morning of May 18, it was clear that the tumors in her chest were preventing her from getting enough oxygen. She wasn't in pain or distress, but was quite weak and things were only going to go downhill rapidly.

It was time to say goodbye. She died just two weeks short of one year from the time the diagnosis was made. She had a great year and kicked cancer's butt for much longer than we thought would be possible. We will miss her forever.