A phase II study of copper-depletion using tetrathiomolybdate (TM) in patients (pts) with breast cancer (BC) at high risk for recurrence: Updated results.

Abstract

2557 Background: The tumor microenvironment (TME) plays a critical role in the spread of tumors. Bone marrow derived VEGFR2+endothelial progenitor cells (EPCs) and copper-dependent lysyl oxidase (LOX) are key in tumor progression. We hypothesized TM-associated copper depletion inhibits tumor metastases by reducing the number of EPCs and other copper dependent (CD) processes in the pre-metastatic niche. These results are an update with longer follow-up. Methods: Phase II study of BC pts at high risk for recurrence, defined as node+ triple negative (TNBC), stage 3 and 4 with no evidence of disease (NED) were enrolled on a trial of CD with TM. Ceruloplasmin (Cp) levels were maintained between 8-16 mg/dl for two years with an extension phase or until relapse. The primary endpoint was change in EPCs measured by flow cytometry before and during treatment. Secondary endpoints included tolerability, safety, PFS and LOXL-2 levels. Results: 75 pts received 2650 cycles of TM on primary and extension study. The median age is 51 years (range 29-66). Forty-five pts have stage 2/3 BC and 30 with stage 4 NED. TNBC pts were 48% and 40% of pts are stage 4 NED. Median Cp level decreased from 28 to 16 (p < 0.0001) after one cycle. Copper depletion was most efficient in TNBC where Cp levels dropped from 23.5 to 13 after one cycle. TM was well tolerated with grade 3/4 toxicities including: reversible neutropenia (2.3%), febrile neutropenia (0.04%), fatigue (0.2%). Five-year analysis showed a decrease in EPC’s (p = 0.004) and LOXL-2 (p < 0.001). At a median follow-up of 6.9 years, the EFS for 75 pts is 75.6%. PFS for 36 pts with TNBC is 79.2%. EFS for stage 2/3 TNBC is 90% and for stage IV TNBC is 66.7%. Conclusions: TM is safe, well tolerated and appears to affect multiple components of the TME creating an inhospitable environment for tumor progression especially in high risk patients such as TNBC. Randomized trials are warranted, especially in patients at high risk for relapse. Clinical trial information: UL1TR000457.