Fears that temporarily suspending breast cancer screening services during the pandemic would create a wave of advanced tumours do not appear to have come true.

NSW suspended screening services for seven weeks in early 2020 to prevent the spread of COVID-19.

A study by the Cancer Institute NSW published on Thursday compared the average tumour size of women who had their mammography screening delayed by the pandemic and those who had not.

In those who waited for testing the average tumour size was 16.2mm, compared with 15.9mm for those who didn't.

The researchers concluded the difference of 0.3mm was not medically "significant" and any additional risk was likely outweighed by the benefits of reducing COVID infections at the time.

"Our retrospective analyses demonstrated no evidence of a substantial change in the size of tumours," the researchers wrote.

The study was published in the Sax Institute's Public Health Research & Practice peer-reviewed journal.

The authors noted the findings were in line with international research that also found short-term interruptions to cancer screening did not result in a wave of diagnoses, particularly when screening services catch up with backlogs quickly.

However, they added the results may not reflect the experiences in other Australian states and territories because of variations in COVID restrictions and lockdowns.