# Early FDG-PET response → chemotherapy omission (HER2+)

Source: https://onco.cc/pairings/pet-adapted-her2-deescalation/  
OnCo record `pet-adapted-her2-deescalation` (Pairing). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

A PET scan after two cycles of antibodies alone identifies women who can be cured without chemotherapy.

## Summary

This diagnostic-therapeutic pairing uses an early FDG PET scan to decide who can omit chemotherapy in HER2-positive breast cancer treated with dual HER2 blockade. After two cycles of trastuzumab and pertuzumab alone, with or without endocrine therapy, a metabolic response on PET predicts a pathological complete response to antibody-only treatment, and that complete response in turn predicts an excellent long-term outcome. In the randomised phase 2 PHERGain trial, PET responders continued the antibodies without chemotherapy and those reaching a pathological complete response skipped it altogether; the trial met its co-primary endpoints. The phase 3 PHERGain-2 trial and similar response-adapted designs such as WSG-ADAPT are now testing the approach more broadly.

## Fields

- Kind: Pairing
- Last checked: 2026-09-07
- Pairs: FDG PET + Dual HER2 blockade
- Type: diagnostic-therapeutic
- Rationale: Metabolic response at 2 cycles predicts pCR to antibody-only therapy; pCR predicts excellent long-term outcome.
- Evidence: Randomised phase 2 meeting co-primary endpoints; phase 3 pending.

## Sources

- ClinicalTrials.gov NCT03161353: PHERGain: https://clinicaltrials.gov/study/NCT03161353

## Connected records

- cancers: [HER2-positive breast cancer](https://onco.cc/cancers/breast-her2-positive/)
- technologies: [FDG PET](https://onco.cc/technologies/fdg-pet/)
- drugs: [Pertuzumab](https://onco.cc/drugs/pertuzumab/), [Trastuzumab](https://onco.cc/drugs/trastuzumab/)
- trials: [PHERGain](https://onco.cc/trials/phergain/)
- terms: [Dual HER2 blockade](https://onco.cc/terms/dual-her2-blockade/)

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