# START-A (UK Standardisation of Breast Radiotherapy, trial A)

Source: https://onco.cc/trials/start-a/  
OnCo record `start-a` (Trial). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

START-A is the dose-finding half of the British experiment that shortened breast radiotherapy. By giving thirteen larger treatments over the same five weeks at two different total doses, it measured how sensitive breast cancer is to the size of each dose, and the answer is what made three weeks and later one week possible.

## Summary

START-A and START-B were run together in 35 United Kingdom radiotherapy centres from 1999 to 2002. START-A kept the overall time at five weeks and varied only the fraction size, comparing 41.6 Gy or 39 Gy in thirteen fractions against the international standard of 50 Gy in twenty-five. Holding the time constant is what makes it a radiobiology experiment rather than a convenience trial: it isolates the effect of fraction size.

At a median 9.3 years, 139 local-regional relapses had occurred among the 2,236 women. Ten-year local-regional relapse was 6.3 percent with 41.6 Gy (95 percent confidence interval 4.7 to 8.5) against 7.4 percent with 50 Gy (5.5 to 10.0), a hazard ratio of 0.91 (0.59 to 1.38, p=0.65), and 8.8 percent with 39 Gy (6.7 to 11.4), a hazard ratio of 1.18 (0.79 to 1.76, p=0.41). Moderate or marked breast induration, telangiectasia and breast oedema were significantly less common after 39 Gy than after 50 Gy; normal-tissue effects after 41.6 Gy and 50 Gy did not differ.

The number that mattered is the one the two doses bracket. Tumour control was slightly better at 41.6 Gy and slightly worse at 39 Gy, while normal tissue improved steadily as the dose fell, which means breast cancer responds to fraction size much as normal breast tissue does. That sensitivity, a low alpha to beta ratio, is the physics behind START-B's 40 Gy in fifteen fractions and FAST-Forward's 26 Gy in five.

## Fields

- Kind: Trial
- Status: positive
- Last checked: 2026-09-25
- Also known as: START A; UK START trial A
- Phase: 3
- Setting: Completely excised invasive breast cancer, pT1 to pT3a, pN0 to pN1, M0, after breast-conserving surgery or mastectomy: 41.6 Gy or 39 Gy in thirteen fractions over five weeks against 50 Gy in twenty-five fractions over five weeks, with local-regional relapse and late normal-tissue effects as the primary endpoints
- Sponsor: Institute of Cancer Research, United Kingdom
- Enrolled: 2236
- Result: Ten-year local-regional relapse 6.3 percent with 41.6 Gy in thirteen fractions, 8.8 percent with 39 Gy and 7.4 percent with 50 Gy in twenty-five, with fewer late normal-tissue effects at 39 Gy.
- Outcomes: Local-regional relapse at 10 years: 41.6 Gy in 13 fractions 6.3% vs 39 Gy in 13 fractions 8.8% vs 50 Gy in 25 fractions 7.4%
- Replication: START-B, run in the same centres, tested 40 Gy in fifteen fractions over three weeks and became the United Kingdom standard; FAST and FAST-Forward pushed the same radiobiology to five fractions.

## Sources

- ISRCTN59368779: https://www.isrctn.com/ISRCTN59368779
- START ten-year results (Lancet Oncology 2013): https://doi.org/10.1016/S1470-2045(13)70386-3

## Connected records

- cancers: [Breast cancer (all types)](https://onco.cc/cancers/breast-cancer/), [HER2-positive breast cancer](https://onco.cc/cancers/breast-her2-positive/), [HR-positive / HER2-negative breast cancer](https://onco.cc/cancers/breast-hr-positive/), [Triple-negative breast cancer (TNBC)](https://onco.cc/cancers/tnbc/)
- technologies: [Hypofractionated radiotherapy](https://onco.cc/technologies/hypofractionated-radiotherapy/), [IMRT / IGRT (modern external beam)](https://onco.cc/technologies/imrt-igrt/)
- institutions: [The Institute of Cancer Research](https://onco.cc/institutions/icr-london/)
- terms: [Alpha/beta ratio](https://onco.cc/terms/alpha-beta-ratio/), [Hypofractionation (fewer, larger radiotherapy doses)](https://onco.cc/terms/hypofractionation/)
- trials: [FAST (5-fraction whole-breast radiotherapy)](https://onco.cc/trials/fast-trial/), [FAST-Forward](https://onco.cc/trials/fast-forward/), [START-B (UK Standardisation of Breast Radiotherapy)](https://onco.cc/trials/start-b/)
- key papers: [The UK Standardisation of Breast Radiotherapy (START) trials of radiotherapy hypofractionation for treatment of early breast cancer: 10-year follow-up results of two randomised controlled trials](https://onco.cc/key-papers/paper-haviland-lancet-oncol/)

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