The discovery of a gene involved in breast development may help in the fight against cancer, scientists say.
The breast development gene was named after a James Bond villain
The gene - named Scaramanga after the three-nippled James Bond villain in The Man With The Golden Gun - was found by an Institute of Cancer Research team.
Researchers said by analysing the gene they would be able to find out more about breast formation and how it is connected to breast cancer.
But experts said more research was needed to examine the cancer link.
When an embryo is developing, the formation of organs is tightly controlled by specific genes.
This process controls the development of two breasts in humans, but sometimes something goes wrong and leads to fewer, extra or misplaced breasts and nipples.
One in 18 people has an extra nipple, which can look like freckles or moles.
But until now little has been known about how this process is governed.
The researchers, writing in the journal Genes and Development, said that the Scaramanga gene regulated the early stages of breast development and influenced the number and position of breasts.
They said they realised the importance of the discovery when they found that the gene produced a protein called NRG3 and that this provides a signal telling embryonic cells to become breast cells.
Lead researcher Professor Alan Ashworth, director of The Breakthrough Breast Cancer Research Centre, said: "By learning more about this gene and the protein it produces, it will allow us to determine how normal breast development is initiated and examine how this is connected with breast cancer.
"While proteins carefully control the development of breast cells in the embryo, inappropriate signals to breast cells during adulthood by these same molecules may cause breast cancer."
Henry Scowcroft, senior information officer from Cancer Research UK, says: "Understanding how our bodies grow and develop holds the key to how normal cells turn into cancer cells."
Dr Mark Matfield, scientific consultant at the Association for International Cancer Research, said while it was an interesting discover, it was "difficult to see the medical implications at this stage".
"The intriguing possibility is whether or not there is any link to the mechanism of breast cancer, but we will need further research into that question before we know the answer."