Systemic Chemotherapies Retain Antitumor Activity in Desmoid Tumors Independent of Specific Mutations in CTNNB1 or APC: A Multi-institutional Retrospective Study

PURPOSE

Determine whether specific CTNNB1 or APC mutations in patients with desmoid tumor were associated with differences in clinical responses to systemic treatments.

EXPERIMENTAL DESIGN

We established a multi-institutional dataset of previously treated patients with desmoid tumor across four U.S. sarcoma centers, including demographic and clinicopathologic characteristics, treatment regimens, and clinical and radiographic responses. CTNNB1 or APC mutation status was determined from prior pathology records, or archival tissue was requested and analyzed by Sanger sequencing and/or next-generation sequencing. Evaluable patients with mutation results were analyzed to determine clinical progression-free survival (cPFS), RECIST 1.1 PFS (rPFS), time to next treatment (TTNT), and overall survival (OS). Kaplan-Meier analysis and Cox proportional hazards regression were performed to identify differences in cPFS, rPFS, TTNT, and OS by mutation subtype, desmoid tumor location, and treatment regimen.

RESULTS

A total of 259 evaluable patients were analyzed for at least one of the survival outcomes, with 177 patients having mutation data. First- and second-line cPFS, rPFS, and TTNT were not significantly affected by mutation subtype; however, APC-mutant desmoid tumors demonstrated nonstatistically significant inferior outcomes. Extremity/trunk desmoid tumor location and treatment with doxorubicin-based, methotrexate/vinca alkaloids and sorafenib regimens were associated with better clinical outcomes compared with surgery or "other" therapies, including estrogen-receptor blockade and imatinib. OS was significantly worse with APC or CTNNB1 negative/other mutations.

CONCLUSIONS

Mutation subtype did not affect responses to specific systemic therapies. APC mutations and nonextremity desmoid tumor locations remain prognostic for worse outcomes, and earlier initiation of systemic therapy for these higher-risk desmoid tumors should be prospectively evaluated. See related commentary by Greene and Van Tine, p. 3911.

E6-AP facilitates efficient transcription at estrogen responsive promoters through recruitment of chromatin modifiers

E6-AP is a known coactivator of the estrogen receptor alpha (ERα), however the coactivation mechanism of E6-AP is not clear. This work was undertaken to elucidate the coactivation mechanism of E6-AP. In order to examine the role of E6-AP in ERα signaling, we knocked-down the expression of E6-AP and examined the transactivation functions of ERα. Knockdown of E6-AP showed reduced mRNA production of the ERα target genes pS2 and GREB1 suggesting that E6-AP is required for their proper transcription facilitated by ERα. In order to study the mechanism(s) by which E6-AP regulates the transcriptional functions of ERα, we performed chromatin immunoprecipitation (ChIP) assays under E6-AP knockdown conditions. Our ChIP data suggest that knockdown of E6-AP leads to decreased recruitment of the histone acetylase p300 to the ERα target gene pS2 promoter as well as reduced histone modifications at the promoter. Although there was reduced p300 recruitment to the pS2 promoter, loss of p300 did not account fully for the loss of histone acetylation. Taken together our data suggest that E6-AP regulates the transactivation functions of ERα in part by complexing with p300 and other chromatin modifying enzymes at target gene promoters to create a transcriptionally active promoter environment.