Prophylactic vs. Reactive Gastrostomy Tube Placement in Patients Treated with Radiotherapy for Head and Neck Cancer

PURPOSE/OBJECTIVE(S)

Radiotherapy (RT) for head and neck cancer (HNC) can cause acute toxicities resulting in weight loss warranting alterative enteral access. Some institutions favor prophylactic gastrostomy tube (GT) placement to prevent malnutrition at the forefront, while others choose to reactively place tubes if nutritional deficits arise. Though prophylactic GT placement may limit on-treatment weight loss, this approach may result in unneeded GT placement and may potentially impact long-term swallowing function.

MATERIALS/METHODS

Patients with HNC treated with CRT from 2018-2021 were reviewed. GT placement prior to CRT (prophylactic [ppx] tube) was performed at the discretion of the treating radiation oncologist. The remainder of patients were treated with reactive (rx) GT placement in the event of on-treatment weight loss approaching 10-15%. Patient, disease and treatment factors were abstracted from the medical record. Primary endpoints were placement of GT in the rx group, weight change at the end of RT, and time to tube removal.

RESULTS

In total, 278 patients were identified; 35 GT-dependent patients and 22 patients with nasal cavity/paranasal sinus cancers were excluded, yielding 221 for analysis. Baseline factors associated with GT group included age, ECOG, baseline swallowing function, primary site, T and N stage, stage group, and treatment year. Treatment factors associated with GT group were: neck target (bilateral v. unilateral/none), concurrent chemotherapy, and total dose. Of the 118 patients in the rx group, 14 (12%) required rx GT placement during or within 30 days of CRT. RT completion rates were similar between groups (95-96%, p = 1). GT was removed at last follow-up in 57% of patients in both groups (p = 1). Percent on-treatment weight loss was -8.9% (SD 6.7) and -7.2% (SD 6.1) for the ppx and rx groups, respectively (p = 0.04). Median Kaplan-Meier estimate of time to GT removal was 7.7 months (95% CI 6.0-11.3) and did not differ between groups (log-rank p = 0.87). Factors associated with the placement of rx GT include: concurrent chemotherapy (yes 20% vs. No 0%, p.0007) and baseline FOIS (5 or less 40% vs. 6 or more 9%, p = 0.02). T stage, N stage, overall stage, postoperative RT, degree of neck irradiation were not associated.

CONCLUSION

Reactive gastrostomy tube placement in patients treated with chemoradiotherapy for head and neck cancer patients is feasible and results in low rates of gastrostomy tube placement. There are no observed differences in on-treatment weight loss between patients treated using a prophylactic versus reactive approach. No differences in time to gastrostomy tube removal were observed.

Degradation of GSPT1 causes TP53-independent cell death in leukemia while sparing normal hematopoietic stem cells

Targeted protein degradation is a rapidly advancing and expanding therapeutic approach. Drugs that degrade GSPT1 via the CRL4CRBN ubiquitin ligase are a new class of cancer therapy in active clinical development with evidence of activity against acute myeloid leukemia in early-phase trials. However, other than activation of the integrated stress response, the downstream effects of GSPT1 degradation leading to cell death are largely undefined, and no murine models are available to study these agents. We identified the domains of GSPT1 essential for cell survival and show that GSPT1 degradation leads to impaired translation termination, activation of the integrated stress response pathway, and TP53-independent cell death. CRISPR/Cas9 screens implicated decreased translation initiation as protective following GSPT1 degradation, suggesting that cells with higher levels of translation are more susceptible to the effects of GSPT1 degradation. We defined 2 Crbn amino acids that prevent Gspt1 degradation in mice, generated a knockin mouse with alteration of these residues, and demonstrated the efficacy of GSPT1-degrading drugs in vivo with relative sparing of numbers and function of long-term hematopoietic stem cells. Our results provide a mechanistic basis for the use of GSPT1 degraders for the treatment of cancer, including TP53-mutant acute myeloid leukemia.

Mutation affecting regulation of synthesis of acetohydroxy acid synthetase in Escherichia coli K-12

Altered regulation of synthesis of acetohydroxy acid synthetase (AHAS) was previously reported in a mutant of Escherichia coli strain K-12. The mutant strain, growing in minimal medium, exhibits a partial growth limiatation and derepression of AHAS, owing to deficient synthesis of isoleucine. The genetic lesion (ilvE503) causing the isoleucine limitation was shown to cause derepression of a valine-sensitive AHAS activity. The derepression effect of the ilvE503 mutation upon synthesis of AHAS was conclusively demonstrated by introducing both the ilvE503 allele and an altered AHAS (ilv-521) into the same cell. Evidence is presented that suggests the presence of multiple genetic regions for synthesis and control of the valine-sensitive AHAS activity.