Phase II study of olaparib in patients with refractory Ewing sarcoma following failure of standard chemotherapy.
BACKGROUND
Preclinical studies have documented antitumor activity of PARP inhibition both in vitro and in vivo, against Ewing sarcoma cells. This study aimed to translate that observation into a clinical trial to assess the efficacy and tolerability of olaparib, a PARP inhibitor, in patients with advanced Ewing sarcoma (EWS) progressing after prior chemotherapy.


METHODS
In this nonrandomized phase II trial, adult participants with radiographically measureable metastatic EWS received olaparib tablets, 400 mg orally twice daily, until disease progression or drug intolerance. Tumor measurements were determined by CT or MRI at 6 and 12 weeks after starting olaparib administration, and then every 8 weeks thereafter. Tumor response determinations were made according to RECIST 1.1, and adverse event determinations were made according to CTCAE, version 4.0. A total of 22 participants were planned to be enrolled using a conventional 2-step phase II study design. If no objective responses were observed after 12 participants had been followed for at least 3 months, further accrual would be stopped.


RESULTS
12 participants were enrolled, and all were evaluable. There were no objective responses (PR/CR), 4 SD (duration 10.9, 11.4, 11.9, and 17.9 wks), and 8 PD as best response. Of the SD, 2 had minor responses (-9% and -11.7% by RECIST 1.1). The median time to disease progression was 5.7 weeks. Further enrollment was therefore discontinued. No significant or unexpected toxicities were observed with olaparib, with only a single case each of grade 3 anemia and grade 3 thrombocytopenia observed.


CONCLUSIONS
This study is the first report of a prospective phase II trial to evaluate the safety and efficacy of a PARP inhibitor in patients with advanced Ewing sarcoma after failure of standard chemotherapy. Olaparib administration was safe and well tolerated when administered to this small heavily pre-treated cohort at the 400 mg BID dose, although the median duration of dosing was for only 5.7 weeks. No significant responses or durable disease control was seen, and the short average interval to disease progression underscores the aggressiveness of this disease. Other studies to combine cytotoxic chemotherapy with PARP inhibition in EWS are actively ongoing.


BACKGROUND
ClinicalTrials.gov Identifier: NCT01583543.
Division of Hematology Oncology, Massachusetts General Hospital, Boston, MA, USA. echoy@mgh.harvard.edu.
Edwin
E
Choy
James E
JE
Butrynski
David C
DC
Harmon
Jeffrey A
JA
Morgan
Suzanne
S
George
Andrew J
AJ
Wagner
David
D
D'Adamo
Gregory M
GM
Cote
Yael
Y
Flamand
Cyril H
CH
Benes
Daniel A
DA
Haber
Jose M
JM
Baselga
George D
GD
Demetri
D000293:Adolescent; D000328:Adult; D000368:Aged; D000970:Antineoplastic Agents / Q000494:pharmacology / Q000627:therapeutic use*; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000627:therapeutic use; D001859:Bone Neoplasms / Q000188:drug therapy* / Q000401:mortality / Q000473:pathology; D003131:Combined Modality Therapy; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010793:Phthalazines / Q000494:pharmacology / Q000627:therapeutic use*; D010879:Piperazines / Q000494:pharmacology / Q000627:therapeutic use*; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; D019233:Retreatment; D012512:Sarcoma, Ewing / Q000188:drug therapy* / Q000401:mortality / Q000473:pathology; D017211:Treatment Failure; D016896:Treatment Outcome; D055815:Young Adult
D000970:Antineoplastic Agents; D010793:Phthalazines; D010879:Piperazines; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; C531550:olaparib