Invasive breast cancer after a diagnosis of ductal carcinoma in situ (DCIS)

This research used data made available via the Office for National Statistics (ONS) Secure Research Service (SRS), which is being expanded and improved with ADR UK funding.

Authors: Dr Gurdeep Mannu, University of Oxford

Date: December 2020

Research summary

This research provided new insight into the incidence and longer-term risks of invasive breast cancer and death in women following their diagnosis for a condition called ductal carcinoma in situ (DCIS). A diagnosis of DCIS means that some cells in the milk ducts in the breast have started to turn into cancer. The condition indicates the abnormal cells are contained inside ducts and have not yet started to spreadⁱ. Investigating whether DCIS is being over-diagnosed and over-treated, the study found that intensive treatment, such as mastectomy and radiotherapy typically led to lower rates of invasive breast cancer.

The incidence of DCIS has increased substantially in recent years, especially following the introduction of breast screening programmes. DCIS accounts for around a fifth of all new breast cancer diagnoses in women and is associated with increased long-term risks of invasive breast cancer and death from breast cancer. While DCIS is typically treated with surgery followed by radiotherapy, concerns with over-diagnosis and over-treatment have raised interest in non-operative management.

Data used

This research created a population based observational cohort study using baseline data from the UK’s NHS Breast Screening Programme data (NHSBSP), which began in March 1998. Initially women aged 50-64 years were invited to attend, and from 2003 the age range was extended to include women aged 65-70 years. The attendance rate for women invited for screening has consistently been over 70%.

The dataset included information on patient related factors (date of screening, date of DCIS diagnosis, age at DCIS diagnosis, any previous cancer diagnoses, region of residence based on the former Cancer Registry regions). The date and site of any subsequent breast cancer registrations as well as the date of emigration and the date and cause of death if relevant were also included. For women screened from April 2000, information was also received on tumour related factors (e.g., tumour size) and treatments (e.g., type of surgery, radiotherapy).

Methods used

The research team analysed outcome data from around 35,000 women in England diagnosed with DCIS by the NHS Breast Screening Programme from its start in 1988 until March 2014. By following up outcomes, they compared rates of invasive breast cancer and of death from breast cancer with the corresponding national rates for women of the same age in the same calendar year.  

The team used a standard epidemiological approach to calculate cumulative expected risks, similarly, using cancer incidence rates for England and mortality rates for England and Wales in five-year age groups and single calendar years. They considered competing risks of death from other causes by using 2014 death rates for England and Wales. For each woman in the study, the length of time from six months after her DCIS diagnosis until the earliest of either invasive breast cancer diagnosis, death, emigration, or 31 December 2014 was calculated. These lengths of time were added together and formed the person-years at risk.

Research findings

The women with DCIS developed invasive breast cancer at a rate more than double that expected from national cancer incidence rates. Of these women, 310 died from breast cancer, around 70% higher than that expected from national breast cancer mortality rates. Increased risk appears to last for at least 20 years after diagnosis.