The treatment of advanced GIST patients is based on imatinib followed with sunitinib in case of resistance/intolerance. However, the median progression-free survival (PFS) on sunitinib is frequently short, and after failure with both imatinib and sunitinib, treatment remains controversial.

Previous studies on GISTs have linked 9p21 alterations to tumor progression (El-Rifai et al. 2000; Kim et al., 2000; Schneider-Stock et al., 2003; Schneider-Stock et al., 2005; Romeo et al. 2009; Haller et al., 2008) but the driver gene was not positively identified (CDKN2A, CDKN2B, or MTAP) (Astolfi et al., 2010; Belinsky et al., 2009; Perrone et al., 2005; Assamaki et al. 2007; Huang et al., 2009). A recent study has shown that homozygous 9p21 deletions target CDKN2A and more specifically p16INK4a 4. Most of the CINSARC genes are known to be under the transcriptional control of E2F. RB1 sequesters E2F, which is released from the complex upon RB1 phosphorylation by CDK4. CDK4 is, in turn, inhibited by p16INK4a. Hence, we hypothesize that alteration of the restriction point via deletion of p16INK4a (and more rarely of RB1: 20% of cases) gene in GISTs is likely to be a causative event that leads to the overexpression of CINSARC genes, which in turn induce chromosome instability and ultimately metastasis. Low p16INK4a expression was associated with response to PD-0332991 in several in vitro tumor model(Konecny et al. 2011; Katsumi et al. 2011; Finn et al. 2009). Considering our molecular data, we believed that PD-0332991 warrants clinical investigation in advanced gastrointestinal stromal tumors with alteration of p16INK4a. This alteration is detectable by comparative genomic hybridization which is a technique highly manageable in the context of routine clinical care and clinical trial.

Main objective was to assess the antitumor activity of PD-0332991 in terms of non-progression at 16 weeks (after centralized review) in patients with documented disease progression while on therapy with imatinib and sunitinib for unresectable and/or metastatic GIST.

Medical Conditions : Adult patients with Advanced Gastrointestinal Stromal Tumors Refractory to Imatinib and Sunitinib

Study design : Exploratory, one-arm, multicenter, phase II clinical trial based on two-stage Simon's design

Main objective : To assess the antitumor activity of PD-0332991 in terms of non-progression at 16 weeks (after centralized review) in patients with documented disease progression while on therapy with imatinib and sunitinib for unresectable and/or metastatic GIST.

Secondary objectives

• To assess the antitumor activity of PD-0332991 in terms of :

  • Objective response rate (ORR) (as per RECIST v1.1 criteria)
  • Progression-free survival (PFS) (as per RECIST v1.1 criteria)
  • Overall survival

• To assess the safety of PD-0332991

Study drug formulation: PD-0332991 is formulated as gelatin capsules of 100 mg and 25 mg respectively. PD-0332991 was administrated orally. PD-0332991 dosed on a flat scale of 125 mg. PD-0332991 was administrated on a 21 days on / 7 days off dosing schedule. One cycle was considered to consist of 4 weeks of PD-0332991 administration.Patients were treated with PD-0332991 until progression of disease, unacceptable toxicity, death or discontinuation for any other reason.

Tumor assessment and response assessed according to RECIST v1.1, with same type of exam in regard of baseline.

All potential sites of tumor lesions (target and non-target lesions) assessed using MRI or CT Scan with IV contrast of the Thorax Abdomen and Pelvis using a 5mm slice thickness with a contiguous reconstruction algorithm (a PET scan is not acceptable for radiological evaluation).

Evaluation were assessed:

• at baseline within 21 days before the first dose of PD-0332991
• at D(28) of Cycle 1, at D(28) of Cycle 2 then every 8 weeks until month six and then every 12 weeks until disease progression or starting other treatment.

Response regarding the first endpoint was assessed by central radiology review. Whenever the criteria of response are met (Complete Response (CR) or Partial Response (PR)), the appropriate imaging tests were repeated at least four weeks later in order to confirm the response.

The decision regarding patient management remained with the local investigator.

optionnal: Fresh tumor biopsies FFPE (Formalin-Fixed Paraffin-Embedded) at screening and at Day 21 of Cycle 1 are encouraged to be collected. Once collected, the samples may be profiled by IHC, and array gene expression analysis

Inclusion Criteria:

1. Male or female patients ≥ 18 years of age

2. Histologically confirmed GIST of any anatomical location and confirmed by the RRePS Network ; positive immunohistochemical staining for c-KIT (CD117); or negative staining for KIT, but with either positive staining for DOG1 or an identified mutation of KIT or PDGFRA gene

3. CDKN2A gene deletion assessed by array-comparative genomic hybridization (array-CGH)

4. Unresectable and/or metastatic disease with documented progression according to modified RECIST criteria (see section 7.2.1.5 of protocol) after 1st line imatinib and 2nd line sunitinib. Progression on the last line of treatment should be confirmed by central review with two radiological assessments identical (CT scans or MRI) obtained at less from 4 months interval within the 24 months before inclusion.

5. At least one measurable GIST lesion according to RECIST (v1.1 Appendix 3). A previously irradiated lesion is eligible to be considered as a measurable lesion provided that there is objective evidence of progression of the lesion prior to starting PD-0332991.

6. A performance status of 0, 1 or 2 according to the Eastern Cooperative Oncology Group (ECOG) scale(Appendix 1)

7. Recovery from Grade 2 to 4 toxicity related to prior line of treatment assessed according to NCICTCAE v.4.0 (Appendix 2)

8. Adequate bone marrow function as shown by:

   Blood absolute neutrophil count (ANC) ≥ 1.5 x 109/L

   1. Blood platelets ≥ 100 x 109/L
   2. Blood hemoglobin (Hgb) > 9 g/dL

9. Adequate liver function as shown by:

   c. Serum or plasma ALT and AST ≤ 3.0 x ULN (regardless of the presence or absence of metastases) d. Serum or plasma total bilirubin: ≤ 1.5 x ULN (excepted for patients with Gilbert's syndrome)

10. Adequate renal function as shown by serum creatinine ≤ 2 x ULN

11. Patients who give a written informed consent obtained according to French and European regulations.

12. Patients affiliated to the French Social Security

Exclusion Criteria:

1. RB1 gene deletion assessed by array-comparative genomic hybridization (array-CGH)

2. Patients who received anti-cancer drugs ≤ 5 days prior to starting PD-0332991

3. Patients who are treated or planned to be treated concomitantly with other cytotoxic or antineoplastic treatments, such as chemotherapy, immunotherapy, biological response modifiers, or radiotherapy

4. Patients with another primary malignancy within 2 years prior to starting the study drug, with the exception of adequately treated in-situ carcinoma of the uterine cervix, or completely excised (R0 resection) basal or squamous cell carcinoma of the skin

5. Patients with a corrected QT interval using Bazett's formula (QTcB) > 470 msec.

6. Current use or anticipated need for food or drugs that are known strong cytochrome P450 (CYP)3A4 inhibitors (i.e. grapefruit juice, verapamil, ketoconazole, miconazole, itraconazole, posaconazole, erythromycin, clarithromycin, tilithromycin, indinavir, saquinavir, ritonavir, nelfinavir, lopinavir, atazanavir, amprenavir, fosamprenavir, nefazodone, diltiazem, and delaviridine)

7. Patients with impairment of gastrointestinal (GI) function or GI disease that may significantly alter the absorption of PD-0332991 (e.g. severe ulcerative diseases, uncontrolled nausea, vomiting, diarrhea, malabsorption syndrome, or extensive (>1m) small bowel resection, inability to swallow oral medications). Prior partial gastrectomy is not an exclusion criterion.

8. Patients with prior complete gastrectomy

9. Any of the following in the previous 6 months: myocardial infarction, severe/unstable angina, coronary/peripheral artery bypass graft, symptomatic congestive heart failure, cerebrovascular accident, transient ischemic attack or symptomatic pulmonary embolism.

10. Patients with any clinically significant medical or surgical condition which, according to investigators' discretion, should preclude participation

    1. i.e. active or uncontrolled infection, uncontrolled diabetes, active or chronic liver disease (cirrhosis, chronic active hepatitis or chronic persistent hepatitis)
    2. hepatitis B or C virus carriers with normal liver function tests, can be included

11. Known diagnosis of human immunodeficiency virus (HIV) infection. HIV testing is not mandatory

12. Patients who are currently receiving anticoagulation treatment with therapeutic doses :

    1. of warfarin or equivalent anticoagulant (e.g. high dose aspirin or clopidogrel or other)
    2. or have an INR >1.5. Treatment with acetylsalicyclic acid 100 mg daily or low molecular weight heparin (LMWH) is allowed

13. Pregnant or breast-feeding women

14. Women of child-bearing potential not employing two effective methods of birth control. Effective contraception must be used throughout the trial and 24 weeks after the end of PD-0332991 (e.g. condom with spermicidal jelly, foam suppository or film; diaphragm with spermicide; male condom and diaphragm with spermicide, oral, implantable, or injectable contraceptives). Women of child-bearing potential defined as sexually mature women who have not undergone a hysterectomy or who have not been naturally postmenopausal for at least 12 consecutive months (i.e. who has had menses any time in the preceding 12 consecutive months), must have a negative serum pregnancy test ≤ 21 days prior to starting study drug.

15. Fertile males not willing to use contraception as stated above

16. Patients unwilling or unable to comply with the protocol.