Interview has been edited for clarity.
How common is breast cancer?
According to Dr. Adami, breast cancer is the most commonly occurring cancer in women, with an estimated two million newly diagnosed cases worldwide in 2017 and over 600,000 deaths.
Overall, breast cancer accounts for 25 percent of all cancer diagnoses among women. Because the incidence of cancer isn’t always well documented all over the world, detailed data about the rates of breast cancer is somewhat uncertain.
Breast cancer is the most commonly occurring cancer in women, with an estimated two million newly diagnosed cases worldwide in 2017 and over 600,000 deaths.
Dr. Adami says that estimates indicate that breast cancer is the most or second-most common (after cervical cancer) malignancy among women, although internationally, rates of breast cancer vary significantly, sometimes by as much as five times.
Breast cancer survival rate
According to Dr. Adami, survival rates also vary widely between geographic regions, with a less favorable outcome in areas of the world with less developed health care systems and lower awareness of breast cancer symptoms.
There is a great opportunity to use modern communication technologies, particularly smartphones, to enlighten women about early symptoms of breast cancer and increase their awareness.
“In developed countries with optimized treatment, outcomes have increasingly improved over the last decades, particularly after the introduction of systemic adjuvant treatment with chemotherapy or hormones. Overall long-term survival rates of 70–80 percent are now commonly seen in developed countries,” says Dr. Adami.
Why is early diagnosis so important?
Dr. Adami says that the impact of early diagnosis is not as straightforward as you might think.
On one hand, women diagnosed in early stages — with small tumors, no metastasis to the armpits, and no distant spread — undoubtedly have much more favorable outcomes than women diagnosed in more advanced stages.
“It is much more controversial, however, whether women who now have a high level of awareness and see a doctor early would have a better outcome if they were diagnosed through mammography screening when they are asymptomatic. This is indeed a highly controversial area,” Dr. Adami says.
It is highly likely that the many healthy habits that reduce the risk of other chronic diseases and numerous cancers also reduce the risk of breast cancer. These include maintaining a healthy weight, consuming alcohol in moderation, being physically active, and refraining from smoking.
He says that recent evaluations of mammography programs in Norway, Denmark, and the Netherlands have failed to document any meaningful reduction in breast cancer mortality attributable to screening. “A minimal, if any, mortality reduction from screening has to be weighed against the harms that include false positive alarms and much more substantial overdiagnosis of non-lethal cancers and lesions that are presumed to be precursors (carcinoma in situ) of invasive cancer,” Dr. Adami explains.
Dr. Adami says that there is no established test that is able to detect breast cancer earlier — before it shows up on a mammogram.
What key things about breast cancer should you know?
“Like all human malignancies, breast cancer develops through a combination of genetic factors, bad luck, and lifestyle,” Dr. Adami explains.
“Although many lifestyle factors are known, the causes of breast cancer are extraordinarily complex and only partially understood. Many of these factors are unrealistic or impossible to modify,” he says.
It is highly likely that the many healthy habits that reduce the risk of other chronic diseases and numerous cancers also reduce the risk of breast cancer. These include maintaining a healthy weight, consuming alcohol in moderation, being physically active, and refraining from smoking.
How common is breast cancer in different countries?
Dr. Adami says, “Even in developed countries — chiefly the U.S. and Europe — we often observe a slowly increasing trend in incidence, which is complex to explain. There was, however, a transient decrease in the early 2000s that has been generally attributed to the documentation that hormonal treatment for menopausal symptoms increases breast cancer risk, which entailed a dramatic drop in the prescription of such drugs.”
Many women with metastatic and incurable cancer can expect a disease remission and indeed live many years.
Some factors that are likely contributing to an increase in breast cancer rates include the growing obesity epidemic. It could also be that breast cancer is being overdiagnosed, as people without any symptoms undergo mammography screening, and non-lethal lumps that would otherwise never be spotted are turning up on mammograms.
What are the chances of breast cancer coming back?
Dr. Adami says that it’s important to distinguish between breast cancer recurring locally and cancer metastasizing to a different part of the body. Local recurrence is often curable through various combinations of surgery, radiotherapy, and systemic treatment.
On the other hand, if breast cancer has metastasized to other areas of the body, a permanent cure is usually not realistic. However, treatments to ease symptoms and relieve pain have become available.
A first-degree family history increases breast cancer risk by about 50–100 percent.
“Many women with metastatic and incurable diseases can expect a disease remission and indeed live many years,” says Dr. Adami.
What’s the best plan of action for people with a family history of the disease?
“A minority of these women have inherited highly penetrant genetic determinants of disease and should ideally undergo genetic testing,” says Dr. Adami.
“There aren’t many rare genetic syndromes that entail such a high risk that preventive mastectomy should be considered. For most people, a first-degree family history [a parent or sibling with breast cancer] increases breast cancer risk by about 50–100 percent,” he continues.
He says that while it may be tempting to seek out more frequent mammograms, research is showing that in areas with access to modern treatment, mammography has little to no effect on breast cancer mortality.
What are the most important factors that affect breast cancer outcomes?
Lots of factors can predict breast cancer outcomes, and new markers of prognosis are constantly being discovered.
“The big determiner is whether the cancer has already metastasized when the person is first diagnosed, which in most cases makes the disease incurable. Although palliative treatment is still possible,” says Dr. Adami.
“In developed countries, only a minority of women are diagnosed at such a late stage. And among them, the most important prognostic factor is whether or not the primary tumor has spread to the axillary nodes [in the armpits],” Dr. Adami says.
He says that until a few decades ago, health care providers typically removed the lymph nodes in the armpits as part of primary treatment. The prognostic outlook often depended on the number of nodes affected and whether tumors had extended through the lymph node capsule.
But because axillary dissection causes substantial side effects, such as arm swelling, stiffness, and nerve damage, the standard procedure now is to examine the sentinel node, which is the first lymph node where cancer cells might spread from a tumor.
What are the current and future directions of breast cancer research?
Dr. Adami says that research on breast cancer biology, causes, and treatment has been ongoing for decades in many different areas. But big discoveries are unpredictable. However, Dr. Adami sees cause for hope.
“I believe the most reasonable answer to this question is that there is a reason for optimism. Enormous efforts are ongoing, and we have seen substantial progress over the last several decades,” Dr. Adami concludes.
History of updates
Current version (24 December 2021)
Medically reviewed by Hans-Olov Adami, MD, PhD, Professor of Epidemiology, University of Oslo, Norway; Past-member of the Nobel Assembly