What is over diagnosis?

The breast cancer screening will also detect tumours or early stages of cancer which would not have been detected without this examination. It detects breast cancer which would not have become fatal without a screening or without treatment. These cases are referred to as over diagnosis and over-treatment.

The mammography screening also detects very early stages of breast cancer or so-called in-situ carcinomas (DCIS). Some of these never would have caused problems for the woman such as being able to feel a lump or other changes to the breast. Even if left untreated the woman would not have died from breast cancer but from another illness. So this treatment would not have been necessary.

However, even if a woman dies from a car accident or a heart attack one month after being diagnosed with invasive breast cancer, by definition this is considered an over diagnosis.

Over-diagnoses are therefore not false breast cancer diagnoses. They are in fact breast mutations or stages of breast cancer which were confirmed as breast cancer by a biopsy.

But since even a biopsy can't predict if a woman’s breast cancer will remain benign for the rest of her life, she will be advised, according to medical guidelines, to undergo treatment based on the type and size of the tumour.

Over-treatment is typically the treatment of early, slow tumours which can often be treated with much milder options than advanced breast cancer. Women typically don't require chemotherapy, the breast can usually be operated on without performing a mastectomy. It's also not necessary to remove affected lymph nodes in the underarms area.

It can not be scientifically proven how often over-diagnoses occur, and can only provide rough estimates. There is much scientific debate over which calculation method is most suitable for estimating the number of over-diagnoses. The brochure every woman in Germany receives along with the invitation to the mammography screening states that out of 1,000 women participating in the screening for 10 years, 5 to 7 women may be over-diagnosed.