In Metastatic Breast Cancer Treatment, Not All CDK Inhibitors Are Equal


Doctors prescribe drugs known as CDK inhibitors to treat some women with estrogen-receptor-positive (ER+) metastatic breast cancer. Research into these drugs is ongoing, and new, promising CDK inhibitor options are on the horizon. Here, I address the current outlook for CDK inhibitors in ER+ breast cancer.

First, some background: ER+ breast cancers comprise about 70% of all breast cancers. The name reflects the fact that cells of these cancers express estrogen receptors (ERs), which are protein features targeted by many treatment strategies for this cancer type. The estrogen receptor (ER) protein is a treatment target not only because “it is there,” but mainly because it drives tumor cell proliferation in ER+ breast cancer. The activity of the ER depends on its binding to the hormone estrogen, and treatments known as endocrine drugs aim to prevent this interaction. Some endocrine drugs inhibit the synthesis of estrogen in the body (e.g., aromatase inhibitors, such as letrozole and anastrozole), and others prevent the interaction of estrogen with ERs (e.g., ER modulators such as tamoxifen, or the pure anti-estrogen drug fulvestrant). The problem of course is that, in metastatic breast cancer, resistance develops to each and every endocrine drug used. Continue reading…


Continuous Low-Dose Ribociclib Active in Advanced Breast Cancer Causes Less Neutropenia

Excerpt:

“Continuous low-dose ribociclib shows preliminary activity, and has an acceptable safety profile as an alternative to intermittent ribociclib dosing when combined with fulvestrant in the treatment of postmenopausal women with hormone receptor (HR)-positive, HER2-negative advanced breast cancer.

“A phase Ib study, presented at the 2016 San Antonio Breast Cancer Symposium, demonstrated a confirmed partial response (PR) of 13.3% in the continuous ribociclib arm, compared with 23.1% in the intermittent ribociclib arm, but a lower rate of high-grade neutropenia in patients receiving continuous dosing of ribociclib.”

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Adding Everolimus to Fulvestrant Improved Outcomes for Postmenopausal Patients With HR-positive Breast Cancer

Excerpt:

“Progression-free survival was more than doubled for patients with metastatic hormone receptor (HR)-positive, HER2-negative breast cancer resistant to aromatase inhibitor therapy by adding everolimus (Afinitor) to treatment with the endocrine therapeutic fulvestrant (Faslodex), according to data from the PrECOG 0102 phase II clinical trial presented at the 2016 San Antonio Breast Cancer Symposium, held Dec. 6–10.

” ‘Endocrine therapy, often with an aromatase inhibitor, is the standard of care for most patients with HR-positive advanced breast cancer,’ said Noah S. Kornblum, MD, assistant professor of medicine at Albert Einstein College of Medicine and attending physician, medicine at Montefiore Einstein Center for Cancer Care. ‘However, over time, resistance to aromatase inhibitors develops and treating patients with aromatase inhibitor–resistant disease remains a challenge.’ ”

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Fulvestrant Bests Anastrozole in Phase III Breast Cancer Study

Excerpt:

“First-line treatment with fulvestrant (Faslodex) led to significantly better progression-free survival (PFS) compared with anastrozole for patients with hormone receptor (HR)-positive advanced breast cancer, according to findings from the phase III FALCON trial reported at the 2016 ESMO Congress.

“Confirming results of an earlier phase II study, the FALCON trial yielded a median PFS of 16.6 months with fulvestrant versus 13.8 months with anastrozole. Moreover, a consistent advantage favoring fulvestrant emerged from a subgroup analysis. The overall advantage appeared to be driven by a substantial difference in PFS among patients without visceral metastases treated with fulvestrant.”

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Targeting Estrogen Receptor Improves Progression-Free Survival in Advanced Breast Cancer

Excerpt:

“Fulvestrant significantly increases progression-free survival in women with hormone-receptor-positive advanced breast cancer, particularly those with less aggressive lower-volume disease, researchers reported at the ESMO 2016 Congress in Copenhagen.

“Fulvestrant is a selective estrogen receptor degrader that targets the function of the hormone receptor so, unlike aromatase inhibitors such as anastrozole, it does not interfere with estrogen levels themselves.”

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FDA Approves New Indication for FASLODEX® (Fulvestrant)

“AstraZeneca today announced that the US Food and Drug Administration (FDA) has approved a new indication expanding the use of FASLODEX® (fulvestrant) to include use in combination with palbociclib. The combination use is for the treatment of women with hormone receptor-positive (HR+), human epidermal growth factor receptor 2 negative (HER2-) advanced or metastatic breast cancer (MBC) whose cancer has progressed after endocrine therapy. FASLODEX has been approved since 2002 as a monotherapy for the treatment of postmenopausal women with HR+ MBC whose cancer has progressed following antiestrogen therapy.

“Estrogen receptor (ER) positive breast cancer is the most common subtype of breast cancer and one of the key drivers of disease progression for this subtype is through the ER. Laboratory studies show that FASLODEX directly targets the ER by blocking and degrading the ER, helping to inhibit tumor growth.”


Drug Combination Slows Breast Cancer Spread

“A combination of two drugs delays progression of advanced, aggressive breast cancer by an average of nine months – working in all subsets of the most common type of breast cancer.

“The combination – of a first-in-class targeted drug called palbociclib, and the hormone drug fulvestrant – slowed cancer growth in around two-thirds of women with advanced forms of the most common type of breast cancer.

“The combination allowed many women with metastatic hormone-receptor-positive, HER2-negative cancer to delay the start of chemotherapy, which is the traditional treatment option in these patients once hormone drugs have stopped working.”


FDA Expands Palbociclib Approval for Breast Cancer

“The Food and Drug Administration (FDA) has granted an expanded indication for the cyclin-dependent kinase 4/6 inhibitor palbociclib (Ibrance). The drug is now approved for use in combination with fulvestrant in women with hormone receptor (HR)-positive, HER2-negative advanced or metastatic breast cancer whose disease progressed following endocrine therapy.

“Palbociclib was initially approved in February 2015 for the treatment of estrogen receptor–positive, HER2-negative metastatic breast cancer, in women who had not yet received endocrine therapy. The new approval was granted under the FDA’s breakthrough therapy designation.

“The additional indication for palbociclib is based on results from the PALOMA-3 trial, which was stopped early in April 2015 after an interim analysis showed benefit in combination with fulvestrant when compared to fulvestrant and placebo.”


ESMO Asia 2015 Press Release: Asian Women with Endocrine-Resistant Breast Cancer Benefit from Combination Therapy

“Data collected in Japanese and Korean patients included in the global PALOMA3 trial provides evidence that combining palbociclib with fulvestrant is an effective strategy to overcome endocrine resistance in women with hormone receptor positive (HR+), HER2 negative (HER2-) advanced breast cancer. The analysis of efficacy and safety of the combined therapy in an Asian population will be presented (1) at the first ESMO Asia 2015 Congress in Singapore, and results are in line with those reported in all patients (both Asian and non-Asian) earlier this year.

“Endocrine resistance is a major clinical issue that makes advanced breast cancer more difficult to treat. Hormone therapy is generally well tolerated and an easy-to-administer option for breast cancer, with demonstrated benefits in patients whose tumours express hormone receptors (HR), particularly the HR+/HER2- subgroup. The ideal option for patients is to be on one endocrine therapy after another, as long as the disease responds or remains unchanged. ‘However, unavoidably, resistance develops in almost all advanced patients a median ten months after the first-line hormonal agent is administered, and a much shorter median time after the second- or third-line hormonal agents, eventually driving patients to switch to the more toxic chemotherapy,’ one of the study authors, Dr. Jungsil Ro, Center for Breast Cancer at the National Cancer Center, Goyang, Korea, said.”