2017 notches up some landmark approvals

With advances in the understanding of cellular pathways, molecular genetics, and immunology, new drugs for cancer are being released at an increasing rate. A variety of novel agents have recently become available for use, generating excitement for patients and oncologists. Keeping track of all of these new agents is increasingly challenging. This brief review will summarize some of the newest drugs, their indications, and benefits (see related article).

Therapies by tumor

Breast cancer

CDK4/6 inhibitors. The CDK4/6 inhibitor palbociclib was approved in 2015 for the treatment of estrogen-positive, HER2-negative advanced breast cancer, and this year, two more drugs in this class – ribociclib and abemaciclib – were approved for the treatment of hormone receptor–positive breast cancer.

Ribociclib (Kisqali) 600 mg daily (3 weeks on, 1 week off) is approved for use in combination with an aromatase inhibitor. In the study on which the approval was based, there was a response rate of 53% for patients in the study group, compared with 37% for those who received aromatase inhibitor alone (progression-free survival (PFS), not reached vs 14.7 months for single-agent aromatase inhibitor).¹ The occurrence of neutropenia seemed to be similar to that in patients receiving palbociclib. However, unlike with palbociclib, ribociclib requires ECG monitoring for QTc prolongation as well as monitoring of liver function tests.

Abemaciclib (Verzenio) has been approved in combination with fulvestrant as well as a monotherapy.² PFS was 16.4 months for abemaciclib (150 mg bid in combination with fulvestrant), compared with 9.3 months for fulvestrant alone, with corresponding response rates of 48% and 21%. As monotherapy, abemaciclib 200 mg bid had a response rate of 20% with a duration of response of 8.6 months.

Tyrosine kinase inhibitors. The tyrosine kinase inhibitor neratinib (Nerlynx) was approved for extended adjuvant treatment of HER2-positive breast cancer after 1 year of adjuvant trastuzumab.³ Given at 240 mg (6 tablets) daily for a year, compared with a no-treatment control arm, it demonstrated an improvement in invasive disease-free survival (DFS) at 2 years from 91.9% to 94.2%, with no difference in overall survival yet noted. It is associated with diarrhea and also requires hepatic function monitoring.
 

Acute myelogenous leukemia

Multiple new agents were recently approved for use in acute myelogenous leukemia (AML), after decades of slow advance in new drug development.

Midostaurin (Rydapt) is an FLT3 inhibitor approved for use in combination with daunorubicin and Ara-C (cytosine arabinoside) for newly diagnosed AML with FLT3 mutations, which occur in about 30% of AML patients.⁴ It is given orally on days 8-21 at 50 mg bid with induction and consolidation.

In the study on which the approval was based, there was a 10% improvement in overall survival for this subset of AML patients who have a typically a worse prognosis. Event-free survival in patients in the study group was 8.2 months, compared with 3 months in the control arm patients, who did not receive the agent. The drug was also approved for aggressive systemic mastocytosis.

Enasidenib (Idhifa) has been approved for AML with an IDH2 mutation in the refractory/relapsed settings.⁵IDH2 mutations are present in about 20% of patients with AML. Given orally at 100 mg daily as a single agent, enasidenib was associated with a 19% complete remission rate. Patients need to be monitored for differentiation syndrome, somewhat similar to what is seen with ATRA with acute promyelocytic leukemia.

Liposomal daunorubicin and cytarabine (Vyxeos) was approved for newly diagnosed therapy- or myelodysplasia-related AML.⁶ This novel liposomal formulation combines two standard agents and is given intravenously on days 1, 3 and 5 over 90 minutes as daunorubicin 44 mg/m² and cytarabine 100 mg/ m². (For a second induction and in lower dose on consolidation cycles, it is given only on days 1 and 3). The liposomal formulation achieved a superior complete response rate compared with the standard 7+3 daunorubicin plus cytarabine regimen (38% vs 26%, respectively) and longer overall survival (9.6 versus 5.9 months) in these generally poor prognosis subsets.

Gemtuzumab ozogamicin (Mylotarg) was initially approved in 2000 but withdrawn from use in 2010 after trials failed to confirm benefit and demonstrated safety concerns. It has now been re-released in a lower dose and schedule from its original label.⁷ This immunoconjugate of an anti-CD33 bound to calicheamicin is approved for CD33-positive AML. Given at 3 mg/m² on days 1, 4, and 7 in combination with standard daunorubicin–cytarabine induction chemotherapy, it improved event-free survival from 9.5 to 17.3 months. When administered as a single agent (6 mg/m² on day 1 and 3 mg/m² on day 8) in patients who were unable or unwilling to tolerate standard chemotherapy, it improved overall survival (4.9 months versus 3.6 months for best supportive care). As a single agent in relapsed AML, given at 3 mg/m² days 1, 4, and 7 and followed by cytarabine consolidation, it was associated with a 26% complete response rate, with a median relapse-free survival of 11.6 months.