Some lumps in breasts can be harmless initially, but with time they become dangerous. The big mystery is how or when they turn life-threatening.

But for one group of tumours, Singapore researchers have unlocked the door leading to the answer. Called fibroepithelial breast tumours, they include two types: fibroadenomas and phyllodes tumours.

The phyllodes tumour is a rare condition that makes up 2 per cent of all breast cancers. Each year, about 60 to 70 women are diagnosed with it at Singapore General Hospital (SGH). It strikes mainly women in their mid-40s and can recur after being removed surgically.

But what makes it menacing is that it can be mistaken for the common non-cancerous tumour called fibroadenoma, which affects one in 10 women.

Though the phyllodes tumour is larger than fibroadenoma - which is usually less than 2cm but can grow up to 3cm in size - the two can look similar under the microscope.

"Sometimes, there are so many overlapping features that one of them could, unfortunately, be a phyllodes tumour but is diagnosed as a fibroadenoma," said Professor Tan Puay Hoon, head and senior consultant at the department of pathology in SGH.

The hospital sees more than 900 cases of fibroadenomas out of about 3,000 cases in the country each year.

But researchers at the SingHealth Duke-NUS Academic Medical Centre have discovered the culprit genes that form fibroadenomas and cause them to advance. Similarly, they have pinpointed the genes behind phyllodes tumours and which cause them to become cancerous.

"The discovery brings hope that we can eventually test for the presence of the culprit genes to identify more accurately these types of breast tumours," said Prof Tan.

These tests could be in the form of an additional genetic test during a biopsy. "Patients can then receive appropriate clinical intervention in a timely manner," Prof Tan said.

While the discovery could overcome the problem of diagnostic mix-ups, the uncovering of how the gene mutates is perhaps more significant. The researchers have successfully figured out the gene mutations that cause fibroadenomas to advance and turn into benign phyllodes tumours, and also the gene mutations that make benign phyllodes tumours cancerous.

These latest findings, published recently in the prestigious international journal Nature Genetics, are based on a study of 79 phyllodes tumours and 21 fibroadenomas.

The researchers plan to study another 1,500 fibroadenomas and phyllodes tumours to further validate their findings, a move they want to complete within a year.

Apart from being used as a diagnostic tool, the mutated genes could also be potential drug targets, the researchers said.

"I think this is where it gets exciting, because when we find potential targets, they become potential targets for therapy," said Dr Ong Kong Wee, head of SingHealth Duke-NUS Breast Centre. "Currently, beyond surgery for malignant phyllodes, really there is little else we can do."