Palbociclib Appears to Prolong Progression Free Survival in Women with Metastatic Breast Cancer

Yesterday researchers at the annual AACR meeting announced the results of a clinical trial of a new drug with activity in some forms of breast cancer. Palbociclib (PD-0332991), a pill developed by Pfizer, was tested in women with metastatic breast cancer cells with estrogen receptors and lacking Her2. These ER+/Her2- tumors represent the most common breast cancer subtype, which is one reason so many people are eying the results of this relatively small, randomized study.

The phase 2 trial, called PALOMA-1 included 165 post-menopausal women with advanced ER+/Her2 negative disease. The research subjects were assigned to take either Letrazole (Femara, an aromatase inhibitor, a drug that inhibits estrogen synthesis) alone, or Letrazole and also the experimental drug, Palbociclib. The study found a highly significant difference in progression free survival (PFS), the intended endpoint: the mean time until disease progressed was 20.2 months among women who took Palbociclib, as opposed to 10.2 months for those assigned to Letrazole alone. The p-value for the difference between the arms (1-sided) was 0.0004. That’s a powerful  result.

But there was no statistically significant difference in overall survival between the two groups, a fact that was irksome to some observers, particularly in the biotech investment world, and to some who were reminded of the Avastin story and its fall-out. Most of the women lived for approximately 3 years after enrolling, with a trend of a few months favoring the Palbociclib arm. Another problem is that over half the patients were recruited to the study based on biomarker results, having to do with cyclin D1 amplification and/or loss of p16. So it could be the results are more relevant to breast cancer patients who have those particular changes. How those molecular features, enriched in the final study population, relate to Palbociclib’s usefulness in breast cancer and other tumor types warrants more evaluation, for sure.

My feeling is that this may prove to be a useful drug, not just in breast cancer. Any medication which interferes with cell growth by blocking cyclin-dependent kinases (enzymes) called CDK-4 and -6 could be useful in quite a few malignancies. The main side effect was suppression of the bone marrow (low blood cells). Some questions I’d like to ask the researchers, and which I hope they’ll address in the Phase III study, is if certain types of mets (e.g. lung vs. bone) or certain molecular subtypes are more tempered by this drug.

As for 10 months of PFS – if it pans out in a formal, published work, that’s valuable. Imagine that you’re 55 years old and living with metastatic breast cancer. A drug that is likely to delay, by most of 2 years, your tumor’s expansion into the lungs (causing shortness of breath), or bones (causing fractures and pain) or liver, and elsewhere can be worth a lot. It’s about the quality of life, whether or not it’s extended.

One final concern is that this study wasn’t blinded, so the doctors’ assessment of how the patients were doing, and the patients’ assessment of how they were feeling,  may have been influenced by their knowing which arm they were on. Also, because this new drug is a pill, some insurance may not cover it – a policy issue that applies to many new cancer drugs.

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FDA Approves Pertuzumab for Advanced, Her2+ Breast Cancer

We’re on a roll for new treatments of the Her2+ form of breast cancer. On Friday the FDA approved Pertuzumab, a monoclonal antibody, for advanced cases. As indicated, the drug would be given along with another monoclonal antibody, trastuzumab (Herceptin) and a chemotherapy, docetaxel (Taxotere) to patients with advanced breast tumors with high levels of Her2.

The new treatment’s brand name is Perjeta. Like Herceptin, this reagent works by attaching to the Her2 receptor on a cancer cell’s surface. But it differs by binding a distinct part of the molecule; its mechanism of action is said to complement that of Herceptin.  You might recall that HER protein family members are complex signaling molecules that span cell membranes. Her1 is the Epidermal Growth Factor Receptor; it’s turned on when bound by its partner, or molecular ligand, Epidermal Growth Factor(EGF). The others are Her2, -3 and -4.

EGFR (Her1) signaling, Wiki-Books image

The science behind drugs that interfere with Her2 receptors and signaling is nicely summarized in a recent, open-access Nature Reviews Clinical Oncology article. Herceptin binds a particular segment of Her2 on the outside of the cell; this leads to failed signaling on the inside, including cell division signals, and causes cell death by several mechanisms. Pertuzumab binds a distinct segment of Her2 in such a way that it can’t form a complex with the related Her3 molecule; this interaction is needed for Her2 to stimulate cell growth.

The FDA’s approval rests largely on results of the CLEOPATRA (Clinical Evaluation of Pertuzumab and Trastuzumab) study, published earlier this year in the NEJM. In that Phase III study, just over 800 patients were randomly assigned to receive a standard regiment – Herceptin in combination with Taxotere plus a placebo infusion, or the Herceptin-Taxotere combination plus Pertuzumab.

The patients who received Pertuzumab did better in terms of Progression Free Survival (PFS, 18.5 months vs. 12.4 months; this difference holds strong statistical merit). There is a trend, also, in terms of Overall Survival: at a median follow-up point of 19.3 months, there were more deaths in the placebo group. But a statistically significant difference was not reached. Toxicity was reported as “generally similar” in the two groups, but there was more diarrhea, dry skin and rashes among those who got Pertuzumab (Table 3). Heart problems, a known toxicity of the Herceptin-Taxotere regimen, were slightly less common with Pertuzumab. Hair loss, presumably from the chemotherapy part of the regimen, was common in both groups.

One curious thing I noticed, in re-reading the January report, is that although the median age for both patient groups was 54 years, the control patients ranged from 27 – 89 in age; those who got Pertuzumab ranged from 22 – 82 years. Although the younger “shift” of Pertuzumab-receiving patients relative to the controls is unlikely to affect the PFS, it’s odd to include an 89 year old patient on an experimental protocol involving infusions of two monoclonal antibodies along with chemo.

This is a super-costly regimen. Like Herceptin, and like the experimental compound antibody, DM1, about which I wrote last week, Perjeta is manufactured by Genentech. As detailed by Andrew Pollack in the NY Times: the wholesale price for Perjeta will be $5,900 per month for a typical woman; Herceptin costs $4,500 per month. So we’re talking about a treatment in which the monoclonal antibodies alone cost over $10K per month. “A typical 18-month course of treatment would be more than $187,000,” he indicated. But if you add on the costs of the Taxotere, drugs like Benadryl and Decadron to minimize allergic reactions, anti-nausea meds, charges for the infusion and monitoring…It’ll be a lot more than that.

As the FDA notes in its press release, production of Perjeta is currently limited due to a technical issue at the Genentech manufacturing plant. Meanwhile, investigators, doctors and patients will have to sort out the relative value of this drug, on top of the others – including pills – for Her2+ disease.

My opinion is not quite formed on this new antibody. The FDA’s decision was based on results from one trial of 808 patients, half of whom didn’t get the experimental drug. Accrual began in 2008; its broad clinical effects, and long-term toxicities, can’t be established yet. It may be, ten years from now, that Perjeta will be used routinely in patients with other, Her2+ kinds of cancer. Or it may be a toxic bust.  How (and if) we’ll test and compare different doses of Perjeta and potential combinations with other drugs, small pills and traditional chemotherapies – which are many – is not clear. You could, for example, combine one or both of the antibodies with a drug like Lapatinib (Tykerb), that inhibits Her2-triggered growth signals inside the cell.

The problem is that oncologists, and facilities including academic centers where revenue is generated by giving drugs by infusion, now have a huge financial incentive to give the Herceptin-Perjeta-Taxotere regimen. This regimen is approved for first-line treatment of metastatic, Her2+ breast cancer; you don’t have to have “failed” another regimen, as was required for the EMILIA trial. As I understand this approval, an oncologist seeing a woman with recurrent or metastatic Her2+ breast cancer could, immediately, prescribe the 3-drug combination.

It’s impressive that the CLEOPATRA folks included an 89 year old patient in the study. But at some point, you have to wonder where we might draw lines. I’ve no answers on that.

All for now, maybe for the week,

ES

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EMILIA Trial: T-DM1 Appears Helpful in Women with Her2+ Metastatic Breast Cancer

This weekend the American Society of Clinical Oncology (ASCO), to which I belong, is holding its annual meeting in Chicago. Some of the biggest buzz has to do with a new breast cancer drug called T-DM1. ASCO just lifted embargo of the relevant abstract.

The new agent is a hybrid of an old monoclonal antibody, Herceptin, that’s chemically attached to DM1, a traditional kind of chemotherapy. The chemo part, DM1 – also known as emtansine – is manufactured by ImmunoGen. It’s derived from maytansine, a compound that binds tubulin, a protein critical for microtubule formation in dividing cells. According to the NCI website, this chemical, which has antibiotic properties, was extracted from an Ethiopian plant, Maytenus serrata.

T-DM1 was designed by linking the DM1 compound to the trastuzumab (Herceptin) antibody. Trastuzumab is old news in breast cancer. It binds a signaling molecule, Her2, that’s expressed at high levels in approximately 1 in 5 breast tumors. The FDA approved Herceptin for use in patients with metastatic, Her2+ breast cancer in 1998 and, for some women with localized, lymph node positive disease, in 2006. In this new, hybrid drug, the antibody works like a tagged, toxic messenger. In effect, the antibody delivers and inserts the chemo into the malignant cell, where it causes cell death.

The new data, from the Genentech-sponsored EMILIA trial, were presented today:

The Phase III study evaluated 991 women with metastatic breast cancer. All participants had tumors with high levels of Her2 (confirmed in a central pathology lab, for the trial). All had disease that progressed despite treatment with Herceptin and, in most cases, other drugs too. After randomization, 978 women received either of two treatments: the experimental agent, T-DM1, every 3 weeks, by intravenous infusion, or a combination of two pills, “XL” – Xeloda (capecitabine) and Tykerb (lapatinib). Median follow-up was just over 1 year – not bad for a study of MBC, but not great, either.

The big news is this: Among the patients who got the experimental drug, T-DM1, the median time until disease progressed was 9.6 month; for those who took the XL pill combination, it was 6.4 months. This different was statistically significant. Although a difference of 3 months may not sound like much – and isn’t – each regimen in the study held the women’s disease in check for over half a year.

It’s striking that T-DM1 was used as a single agent. Most chemotherapy drugs, like those for HIV, work best in combination; it could be that we’ll see more powerful results in a few years, once we learn how to optimally combine drugs for women with Her2+ breast cancer.

As far as overall survival, the initial results seem quite favorable. Among women on the study for 2 years, 65 percent were alive who received T-DM1; among those taking the XL regimen, 47 percent were alive at 2 years. (The statistical details for this comparison are not available; evidently it was of weak significance.) The problem is – if only a few patients were analyzed “so far out” on the survival curves, the difference observed between the two study arms might be random. Still, and independently of the comparison, survival of 65 percent at 2 years in this patient group is (sadly) impressive, especially if it comes by a single agent with comparatively few side effects.

The main T-DM1 toxicities were low platelets and abnormal liver function, which were, reportedly, reversible. The XL combination caused more toxicity, overall, including diarrhea, hand-foot syndrome and nausea.  A much greater fraction of women on the XL arm (53 and 27 percent, respectively for Xeloda and lapatinib) needed dose reductions, as compared to the T-DM1 (16 percent had dose reductions due to toxicity). Evidently hair loss isn’t an issue for women who get T-DM1, which is nice.

My main, initial concerns are two:

First, the study, though randomized, is not “blinded,” and can’t be.  It’s impossible for women who are getting an intravenous drug, and their doctors, not to know that they’re not on the pill study arm. Although there were independent evaluators of progressive disease, which is a far more subjective measurement than overall survival, progression free survival can be influenced by the doctors’ and patients’ knowing they’re getting the T-DM1. That said, the initial, observed difference in overall survival – a clear, objective measurement – is impressive.

If these trial results, published in abstract form, pan out, and the quality of patients’ lives is maintained, that’d be helpful to as many as 1 in 5 women with MBC. It is plausible that an antibody like Herceptin that targets the tumor cells could, in fact, “deliver” the chemo effectively into the cancer cells with relatively low toxicity. And if the women are feeling better, which is hard to know from an abstract, great.

My second concern is how this drug will mesh with others now available and in the pipeline for patients with Her2+ disease. In a December, 2010 editorial in the JCO, two clinical investigators wrote: “the unique aspect of T-DM1 is clearly its high clinical activity by itself, without the need of concomitant additional systemic chemotherapy.” They’re right. The question – as considered by those authors – is how T-DMI will be used in the context of expanding treatment options for women with Her2+ breast cancer. This is an expensive (price not yet known) monoclonal antibody-conjugate that’s necessarily given by infusion. Testing this drug against all the other current and up-and-coming alternatives, in varying combinations and doses, will be tricky. The trials alone will cost big bucks, besides toxicity and women’s lives.

These EMILIA results are promising for some women with MBC and, possibly, patients with other cancer forms in which Her2 is expressed. Unfortunately, it’s unlikely to help those women with breast cancer whose tumors that lack Her2+.

I’ll write soon about this new class of oncology drugs – antibodies conjugated to chemotherapies, as a group.

All for now,

ES

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A Picture of Periwinkle

Periwinkle plant – the source of Vincristine, a chemotherapy 

Dear Readers,

Your author has been busy writing other things, and revamping this site. Medical Lessons is, if nothing else, a work in progress.

For this week, I thought I’d simply share this image of periwinkle, Catharanthus roseus. From this plant comes an old chemotherapy drug,  called Vincristine (Oncovin). When I practiced, I used this agent to treat people with lymphoma, some forms of leukemia, Kaposi’s sarcoma and, rarely, patients with life-threatening cases of low platelets from an immune condition called ITP.

All for now,

ES

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