Cancer and other chronic disease sufferers will be hit with significant advance costs for medical imaging and other pathology testing under the government's proposed $7 GP co-payment, according to evidence given to a parliamentary committee on Wednesday.

The Australian Diagnostic Imaging Association has warned that previously undiscussed impacts of the fee mean people with the greatest need to get access to complex medical services will be the worst affected.

And many will remain worse off even after rebates are received.

The ADIA says a person suffering liver cancer will be hit with a fee of more than $1200 for scans, consultations and pathology and this figure will climb to more than $2200 if that cancer has metastasised, that is, spread beyond the liver.

In the first case, the cancer sufferer will be up to $264 worse off over a year and in the second case up to $678 worse off, according to the group's modelling.