Several studies have shown that dense breast tissue can hide breast cancer lesions that other modalities such as ultrasound and MRI can help uncover.

A similar bill sponsored by Simitian was vetoed by Gov. Jerry Brown last year despite broad bipartisan support, Simitian said in a statement introducing SB 1538. The senator said he is talking with the governor to look for a path forward for the new bill.

Since last year's veto, Virginia has passed a similar dense-breast notification statue that has led to a 100% increase in the detection of women with dense breast tissue, the statement said; similar laws have already passed in Connecticut, Texas, and Virginia, and legislation is pending in 15 states.

The new bill requires that information already shared between doctors also be shared with the patient herself, Simitian said. If passed, SB 1538 would require that women with dense breast tissue be informed of the following after a mammogram:

• They have dense breast tissue
• Dense breast tissue can obscure abnormalities such as cancer on a mammogram
• They may wish to discuss the potential value of additional screening with their doctors

Such a notice to patients can save lives, the statement continued, and it also saves money because treating early-stage breast cancer is much cheaper than fighting advanced cases.

In 2011, a Mayo Clinic study found that in women with dense breast tissue, 75% of cancers are missed when mammography is used alone. Both dense breast tissue and breast cancers can appear white on mammography, making it difficult to distinguish between the two.