Gastrointestinal toxicity of vorinostat: reanalysis of phase 1 study results with emphasis on dose-volume effects of pelvic radiotherapy

Radiat Oncol. 2011 Apr 8;6:33. doi: 10.1186/1748-717X-6-33.


Background: In early-phase studies with targeted therapeutics and radiotherapy, it may be difficult to decide whether an adverse event should be considered a dose-limiting toxicity (DLT) of the investigational systemic agent, as acute normal tissue toxicity is frequently encountered with radiation alone. We have reanalyzed the toxicity data from a recently conducted phase 1 study on vorinostat, a histone deacetylase inhibitor, in combination with pelvic palliative radiotherapy, with emphasis on the dose distribution within the irradiated bowel volume to the development of DLT.

Findings: Of 14 eligible patients, three individuals experienced Common Terminology Criteria of Adverse Events grade 3 gastrointestinal and related toxicities, representing a toxicity profile vorinostat has in common with radiotherapy to pelvic target volumes. For each study patient, the relative volumes of small bowel receiving radiation doses between 6 Gy and 30 Gy at 6-Gy intervals (V6-V30) were determined from the treatment-planning computed tomography scans. The single patient that experienced a DLT at the second highest dose level of vorinostat, which was determined as the maximum-tolerated dose, had V6-V30 dose-volume estimates that were considerably higher than any other study patient. This patient may have experienced an adverse radiation dose-volume effect rather than a toxic effect of the investigational drug.

Conclusions: When reporting early-phase trial results on the tolerability of a systemic targeted therapeutic used as potential radiosensitizing agent, radiation dose-volume effects should be quantified to enable full interpretation of the study toxicity profile.

Trial registration: NCT00455351.

Publication types

  • Clinical Trial, Phase I
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aged
  • Aged, 80 and over
  • Antineoplastic Agents / adverse effects*
  • Combined Modality Therapy / adverse effects
  • Gastrointestinal Tract / drug effects
  • Gastrointestinal Tract / radiation effects
  • Humans
  • Hydroxamic Acids / adverse effects*
  • Intestinal Neoplasms / therapy*
  • Intestine, Small / radiation effects*
  • Maximum Tolerated Dose
  • Middle Aged
  • Pelvis / radiation effects
  • Radiotherapy / adverse effects*
  • Radiotherapy Planning, Computer-Assisted
  • Vorinostat


  • Antineoplastic Agents
  • Hydroxamic Acids
  • Vorinostat

Associated data