Breast cancer tumors found today tend to be smaller than those found in the past, new research shows.

That may be one more reason why more U.S. women are surviving breast cancer, write Elena Elkin, PhD, and colleagues in the journal Cancer.

They checked a U.S. cancer registry for data on the size of newly found breast cancers from 1975-1999. Smaller tumors accounted for more breast cancer cases as time went by. That was true for all stages of breast cancer, writes Elkin, who works at Sloan-Kettering Cancer Center in New York.

Read WebMD's "What Women Want to Know Before 1st Mammogram"

Breast Cancer Survival Improving

Breast cancer is the most common cancer among American women, except for nonmelanoma skin cancers. Breast cancer is most common in women older than 50.

Breast cancer is also the No. 2 cause of cancer deaths for American women, but breast cancer death rates have been dropping.

In 1975, about 31 out of 100,000 women died of breast cancer. In 2001, that number had dropped to about 26 out of 100,000 women, write Elkin and colleagues.

Today, there are a little more than 2 million U.S. women who have been treated for breast cancer, according to the American Cancer Society.

Read WebMD's "Learn More About Breast Cancer Screening"

3 Reasons Why?

Breast cancer treatments have drastically changed since the 1970s. For instance, tamoxifen, a drug that's widely used to help prevent the return of estrogen-sensitive breast cancer, wasn't around back then. Surgical strategies have also changed to preserve the breast whenever possible.

Health experts have also ramped up breast cancer screening efforts. Early detection can greatly improve a woman's odds of surviving breast cancer. The first national guidelines on mammography were issued in the late 1970s, write Elkin and colleagues.

Smaller tumors could be a third advantage, the researchers note.

How do those three factors -- new treatments, increased screening, and smaller tumors -- rank in importance? The researchers don't have a verdict on that point, but they want to make sure tumor size gets recognized.

Read WebMD's "The Latest Treatments for Breast Cancer"

Breast Health Screening

Most women will not develop breast cancer, much less die of it. Still, don't take a good trend for granted. See a doctor about any breast lumps or health concerns.

The American Cancer Society recommends annual breast exams by a doctor for all women in their 20s and 30s and annual screening mammograms for women aged 40 and older.

The CDC's screening mammogram recommendations are a little different -- every one or two years for women aged 40 and older.

Many women spot breast problems themselves, though medical experts disagree about whether self-exams save lives. In some cases, ultrasound may be used along with other tests to check breast lumps -- most of which are not cancer.

Read WebMD's "The Breast Cancer Gene: What Should You Do?"

By Miranda Hitti, reviewed by Brunilda Nazario, MD

SOURCES: American Cancer society: "Can Breast Cancer Be Found Early?" CDC: "National Breast and Cervical Cancer Early Detection Program: Saving Lives Through Screening -- 2004/2005 Fact Sheet." WebMD Medical Reference from Healthwise: "Breast Self-Examination -- Topic Overview." WebMD Medical News: "Cancer Risk of Benign Breast Lumps Studied."