Those aged over 50 who have only the lump removed, followed by radiotherapy, are almost a fifth more likely to survive the illness than patients who lose the whole breast.
Many women diagnosed with breast cancer choose to have a mastectomy thinking it will remove the tumours as quickly as possible and give them the best chance of survival.
But the results of a ten-year research project by academics show that a less radical form of treatment – breast conservation surgery – is more effective.
It involves taking away the affected lump and then administering high doses of radiotherapy over a course of five or six weeks to ensure any remaining cancerous cells are killed, the 'Daily Mail' reported.
Researchers from Duke University in North Carolina looked at the records of 112,154 women diagnosed with breast cancer between 1994 and 2004.
Around 55 per cent had breast conservation surgery and 44 per cent had a mastectomy.
The study shows that women who had breast conservation surgery were 13 per cent more likely to survive the illness.
But the results were even more promising in women over 50 whose survival odds were 19 per cent higher than those who had mastectomies.
It also found that women of all ages who had breast conservation surgery were a fifth less likely to die from other causes such as heart disease.
This study looked only at women diagnosed with breast cancer early – known as stages one or two. It did not include patients with advanced forms of the illness.
Experts believe radiotherapy may be far more effective at killing all cancerous cells than removing the entire breast.
"Our findings support the notion that less invasive treatment can provide superior survival to mastectomy in stage one or stage two breast cancer," lead researcher Dr E Shelley Hwang, of the Duke Cancer Institute in North Carolina, said.
"Given the recent interest in mastectomy to treat early stage breast cancers, despite the research supporting lumpectomy, our study sought to further explore outcomes of breast-conserving treatments in the general population comparing outcomes between younger and older women," Hwang said.
The study was published in the journal Cancer.