Size alone should not determine biopsy decision, RSNA study finds

Radiologists will often not biopsy small lesions because they assume the lesions are benign. But the decision to do so could mean missing malignant cases, according to a scientific session presented Sunday at the RSNA 2009 meeting.

Previously published literature shows a low malignancy rate for small MRI-detected masses, but a new study presented by Dr. Meera Sekar, a radiologist in Jamaica Plain, MA, shows even small lesions can be malignant.

In the study, Sekar and colleagues looked at 68 masses detected on MRI. Of all the masses, 36 were 5 mm and 32 were 3 to 4 mm. Biopsy revealed malignancy in 15 masses, for an overall malignancy rate of 22%. Of all the masses less than 5 mm, nine were malignant.

The decision to biopsy lesions less than 5 mm in size detected via MRI should be made based on MRI features and patient risk factors, Sekar said.

"No difference in proportion of malignancies was found based on shape or margins," she said.

However, there was a higher proportion of malignancies in patients who had MR for follow-up of a previous MRI finding and those with washout kinetics, she said.

"Radiologists should take the small lesions seriously," said Dr. Elizabeth Morris, moderator of the session.

Lesions less than 5 mm are not always benign; cancers have to grow and their size can start at something as small as 5 mm, said Morris, director of breast MRI and breast imaging research at Memorial Sloan-Kettering Cancer Center in New York.