Multimodal approach to the treatment of patients with radioiodine refractory differentiated thyroid cancer and metastases to the central nervous system

The diagnosis of central nervous system metastases in patients with radioiodine refractory differentiated thyroid cancer is a late and rare event that occurs in less than 1% of patients. Definitive conclusions on the overall clinical management cannot be drawn due to the limited number of patients included in retrospective series or post hoc analysis from clinical trials. However, most data show a trend to an increased benefit from a multimodal approach. Local treatment based on surgical and/or radiation techniques is highly encouraged for symptom control and to reduce tumor burden in this location despite a high risk of clinical complications. In addition, systemic treatment with novel tyrosine kinase inhibitors has demonstrated activity in this subgroup of patients, improving an otherwise unfavorable prognosis.

The PALBONET Trial: A Phase II Study of Palbociclib in Metastatic Grade 1 and 2 Pancreatic Neuroendocrine Tumors (GETNE-1407)

LESSONS LEARNED

Palbociclib demonstrated no detectable activity in molecularly unselected and heavily pretreated patients with advanced grade 1/2 pancreatic neuroendocrine tumors. Predictive biomarkers that improve patient selection should be investigated in future studies of palbociclib.

BACKGROUND

Palbociclib, a CDK4/6 inhibitor, has shown in vitro activity in pancreatic neuroendocrine tumor (pNET) cell lines. Here we prospectively assessed the activity and safety of palbociclib in monotherapy in metastatic refractory pNETs.

METHODS

This was a nonrandomized, open-label, phase II study of patients with metastatic grade (G)1/2 pNETs recruited from 10 centers in Spain. Palbociclib 125 mg was orally administered once daily for 21 of 28 days until disease progression or unacceptable toxicity.

RESULTS

Twenty-one patients were included; 52.4% were men, and median age was 57.4 years (range, 37.4-73.4). Patients had previously received a median of three prior lines of systemic therapy (range, 1-10) for advanced disease (somatostatin analogues, 71.4%; sunitinib, 81.0%; everolimus, 47.6%; chemotherapy, 47.6%). Nineteen patients were evaluated for objective response rate (ORR), with a median follow-up of 12.4 months (range, 7.53-19.33). No objective and confirmed responses were observed (0%); 11 (57.9%) patients had stable disease, and 6 of them lasted more than 6 months; 8 (42.1%) patients had disease progression as best response. Median progression-free survival (PFS) was 2.6 months (95% confidence interval [CI], 0-14.4) and median overall survival (OS) was 18.7 months (95% CI, 7.4-29.9; Fig. 1). Most frequent toxicities of any grade were asthenia (76.2%), neutropenia (42.9%), diarrhea (33.3%), and nausea (33.3%). Five (23.8%) patients developed G3-4 neutropenia and two (9.5%) patients developed G3-4 thrombocytopenia.

CONCLUSION

Lack of activity was observed with palbociclib as a single agent in molecularly unselected and heavily pretreated patients with advanced G1/2 pNETs.