Researchers have found genes associated with breast size, three of which co-relate to breast cancer.

"The findings in this study show that some of the same biological pathways underlie both normal breast growth and breast cancer. Some studies have found that larger breast size as a young woman is associated with a slightly higher risk for breast cancer. The genetic factors we found support this concept that breast size and breast cancer are related," said Nicholas Eriksson, lead author of the study.

For the study, researchers analyzed data from more than 16,000 females of European ancestry. They compared their answers to survey questions including bra cup size and bra band size to genetic data at millions of single-nucleotide polymorphisms.

Single-nucleotide polymorphisms (SNPs) are variations that occur in DNA when a single nucleotide in the genomic sequence is altered. SNPs are studied because scientists believe that these variations will help them find multiple genes associated with cancer, diabetes, heart disease among many others. 

SNPs only show that a person might be at risk and it doesn't mean that all those who have a particular SNP will be affected by the disease/condition.

"These results provide insight into the genetic factors underlying normal breast development and show that some of these factors are shared with breast cancer. While these results do not directly support the known epidemiological relationships between breast size and cancer, this study contributes to a better understanding of the subtle interactions between breast morphology and breast cancer risk," concluded Eriksson.

Breast morphology like density has been associated with increased risk of breast cancer. But, there is no clear links between breast size and cancer risk.

The study is published in BMC Medical Genetics.