It’s been six months since I started Ibrance (generic name: palbocyclib), the CDK-4/6 inhibitor drug I take in combination with letrozole, as my first-line treatment for metastatic breast cancer. While I’m actually midway through cycle 7 at the time I’m writing this, each cycle is 28 days, so six full months was Wednesday, July 18, 2018.
But let’s back up for a minute with a little background on Ibrance. As I mentioned, Ibrance is a CDK-4/6 (cyclin-dependent kinase) inhibitor, which means that, in very abbreviated terms, it prevents over-proliferation of an enzyme that fuels cancer cells, and it is used to treat hormone-positive metastatic breast cancer in postmenopausal women. My breast cancer is strongly estrogen-receptor positive, meaning that it is fueled by the production of estrogen in my body. It is also very weakly progesterone-receptor positive. Because the production of estrogen is driven my ovaries, I was put into chemical menopause in December 2017, at the onset of my treatment. My current treatment entails two shots every four weeks: Lupron to shut down the estrogen production in my ovaries and maintain menopause, and Xgeva to assist the healing and strength of my bones, due to my bone metastases. In addition to these monthly shots, I take letrozole, an aromatase inhibitor (which aids in removing the remaining estrogen from my body, produced outside of my ovaries) and Ibrance. I take Ibrance for three weeks, then stop the drug for the fourth week, which allows my body to have a break from the drug and boost my immune system. In addition to the prescribed drugs, I also take two anti-depressant drugs to help with mood regulation and other menopause symptoms (both due to the onset of menopause and the largely challenging lifestyle of metastatic cancer), and two supplements: vitamin D, which further helps my bone integrity, and an iron supplement, which I take in conjunction with Ibrance: 3 weeks on, 1 week off. This is the supplement regimen I have found works best for me, and all of my doctors are both aware of this regimen and are supportive of it.
Ibrance is a very new drug, and had only been on the market for about 3 years when I started it. It made an impressive showing in clinical trials: as of December 2017, it showed to improve the mean progression-free survival time (the metric used to measure how long a drug is effective at keeping metastatic breast cancer stable until the cancer begins to grow again) from 14.5 months to 27.6 months, when used with letrozole (an aromatase inhibitor), versus taking letrozole plus a placebo. (Source: Pfizer). In lay terms, this finding indicates that on average, when someone only takes letrozole, the cancer doesn’t progress for about 14 months, whereas when someone takes Ibrance with letrozole, their cancer stays stable and does not progress for about 27 months. This statistic does not fully encompass the variables that can, and do, affect metastatic breast cancer progression and survival. For example, the locations of metastases (in the bones, like mine, versus in the lung, liver, or brain), the therapies an individual has taken for breast cancer prior to this treatment, and the number of recurrences an individual has had should all be taken into consideration, although finding the information in which these categories are broken down can be difficult to find. Further, This number indicates only the mean, or average, length of progression-free survival. As with any statistic, there are numbers on either side of the average which represent individuals who experienced both much longer periods of progression-free survival, as well as individuals who experienced significantly shorter periods of progression-free survival while taking Ibrance.
Ibrance has, thus far, been a generally positive experience for me. The menopausal symptoms from the lupron have been challenging – clearly, no one likes hot flashes, and the Xgeva has given me some minor tooth sensitivity. I’ve experienced a small bit of joint discomfort and stiffness on letrozole, and I am much more fatigued than I have been in the past. Events from which I can generally bounce back within a day or two of rest now can cause me to need quite a bit more sleep and rest than I would have needed pre-cancer. I am much more sensitive to the sun and heat than I was before, and I have had about a 25 pound weight gain, primarily due to the menopausal changes. The biggest side effect I have experienced has been my reduced immune system function. I do blood work each month when I see Dr. G, and, while my blood work has generally looked good, my immune system (monitored by the number of white blood cells in the sample, among other metrics) definitely takes a hit with Ibrance. Having a two-year-old in preschool means that a lot of new and interesting germs come home with us, and my son and I have always been fairly susceptible to colds and upper respiratory infections. We have had at least five or so, several of which required treatment with antibiotics, and one of which needed prednisone to clear it up completely. In addition, after the third respiratory infection, I had to take an additional week off of Ibrance in order to allow my body to clear up the infection. I can’t stress enough both how important it is to have a team in which you have tremendous trust, as well as a team who has open and available lines of communication. By the third respiratory infection, we began seeing a pattern, and Dr. G and her team developed a game plan with me so that we could address future illnesses at the onset, and keep them from becoming a several-weeks-long ordeal.
I am often asked how long I intend to remain on this line of treatment. One of the poorly-understood aspects of metastatic breast cancer is the fact that I will be on some sort of treatment for the rest of my life, unless some new development comes along and completely cures metastatic breast cancer. Even then, I will likely continue to be monitored with regular PET scans, as I am now. So far, I have had two PET scans since starting Ibrance: the first scan showed a significant decrease in cancer burden, and the second showed complete stability (no increase or decrease in any tumors in my body). This is all great news, six months in, and I am hopeful that I will continue this treatment for a long time.