Breast cancer

Why are there fewer HER2 positive breast cancers in screen-detected patients?

Screen-detected breast cancers have significantly lower rates of HER2 positivity which may explain the survival advantage in women diagnosed following mammography compared to those diagnosed with symptoms.

A study of more than 100,000 cases of invasive breast cancer from the BreastSurgANZ Quality Audit has shown quite different molecular profiles in screen-detected versus other breast cancers.

It found 89.3% and 78.8% of screen-detected breast cancers were ER+ and PR+ respectively compared to 80.3% and 69.8% of other breast cancers.

Only 11% of screen-detected cancers were HER2 positive compared to 15.6% of other breast cancers.

Correspondingly, rates of luminal B and HER2-enriched subtypes were lower in screen-detected than other breast cancers (7.6 and 3.5% v 9.8 and 5.8% respectively).

Rates of luminal A subtype was significantly higher in screen-detected than other breast cancers (82.3 v 71.4%) while the basal-like subtype was less common in screen-detected than other breast cancers (6.7 v 13.0%).

“Since HER2 positivity has been shown to be associated with the worse survival expectations in both luminal and non-luminal breast cancers, the paucity of HER2-positive cancers in screen-detected patients goes some way in explaining their superior survival,” the study said.

The study also found tumour size was significantly smaller in screen-detected breast cancer (16.8 v 25.4mm) and screen-detected cases had a higher likelihood of node-negative disease (75.4 v 58.9%).

The researchers suggested method of detection should be incorporated into prognostic models as has already been done in the Predict model.

“If screen detection is confirmed as an independent prognostic factor, this information should be incorporated in clinical decision aides so as to tailor systemic therapies to women who stand to gain the most benefit from such interventions.”

For example, and according to the 2017 St Gallen conference, women with luminal B cancers and limited nodal involvement might be candidates for avoiding chemotherapy.

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