Heard of ductal carcinoma in situ or DCIS? What does Stage 0 breast cancer mean and how is it treated?

Singaporean singer Joanna Dong recently went public with the news that she was being treated for ductal carcinoma in situ (DCIS), or Stage 0 breast cancer. In a later Instagram post, she said her doctors subsequently discovered a 7mm tumour and she had Stage 1 breast cancer.
You’ve heard of Stage 1 breast cancer, but what is Stage 0 breast cancer?  
DCIS is referred to as Stage 0 cancer, a precursor to breast cancer. Dr Celene Ng, who heads the breast surgery division at Alexandra Hospital, said DCIS is the earliest detectable stage of breast cancer – it accounts for 25 to 30 per cent of breast cancer in all Singapore women.
“A diagnosis of DCIS is equivalent to a diagnosis of breast cancer,” said Dr Samuel Ow, senior consultant at the Department of Haematology-Oncology at the National University Cancer Institute, Singapore (NCIS). 
In DCIS, the breast cancer cells are confined to the milk ducts in the breast, said Dr Ng. “The cells lining the breast ducts become very abnormal but have not invaded the lining of the duct to involve the neighbouring tissues yet.”
Dr Ong Kong Wee, medical director of K W Ong Breast and General Surgery Clinic, said DCIS cancer cells lack two important features of Stage 1 breast cancer: The ability to invade and destroy the surrounding healthy tissues, and the propensity to spread via the blood vessels and lymphatic ducts.
To become cancerous, cells go through a progression of stages. DCIS is the stage of change that comes right before the final change into cancer, added Dr Ng.
ETHNICITY MAY PLAY A PART IN YOUR RISK
There is no clear indication that one’s ethnicity might increase a woman’s risk of getting breast cancer although one local study seems to point to it.
A 2021 study of the Singapore Breast Cancer Cohort, which evaluated risk factors and genetic markers of Singapore women, found that the breast cancer rate in Chinese women was higher compared with Malays and Indians.
Dr Ong said the underlying reasons are unclear, although it may be related to childbearing, breastfeeding and obesity, based on the information in the study. 
The same study also found that Malay women have the worst five-year overall survival rate (58.5 per cent) among the three ethnic groups, showing symptoms at a younger age as well as presenting with more advanced stages and more aggressive tumours.  
EARLY DETECTION IS CRUCIAL   
“DCIS accounts for more than 30 per cent of breast cancer in younger, pre-menopausal women”, said Dr Ong.
According to NCIS’ Dr Ow, if left untreated, 25 to 60 per cent of DCIS can become invasive breast cancer (where the cancer has spread from the breast to the surrounding tissue).
This is why regular checks, in the form of breast self-examination (BSE) and mammograms, are crucial.
As DCIS tends to be asymptomatic, the best way to detect it is through a mammogram, said Associate Professor Lim Geok Hoon, head of the KK Breast Department at KK Women’s and Children’s Hospital (KKH). A mammogram is currently still the best screening test for breast cancer, she said.
In fact, the vast majority of DCIS is detected via mammogram screening, added Dr Ong.
In Singapore, mammograms are recommended for women aged 40 and above. Women between 40 and 49 years old should get one annually, and this can be reduced to once every two years after they turn 50.  
Alexandra Hospital’s Dr Ng said that women who undergo regular age-appropriate mammographic screening are “more likely to be diagnosed with breast cancer at the DCIS pre-cancerous stage with better survival outcomes”.
From the age of 20, get into the habit of doing monthly BSE, five to seven days after your menses. Post-menopausal women can do their BSE on the same day of every month, advised Assoc Prof Lim.
THE SYMPTOMS OF DCIS 
Finding a breast lump is one of the most prevalent signs of DCIS, especially in women under 40, said Dr Ng.
Other symptoms of DCIS include bloody nipple discharge or skin changes, similar to signs of breast cancer, added Dr Ow.
Less common is a persistent rash called Paget’s disease of the nipple (or of the breast), which appears as eczema-like changes to the skin of the nipple and areola. “This skin change, unlike dermatitis, is persistent despite topical medical treatment,” said Dr Ng.
TREATMENT FOR DUCTAL CARCINOMA IN SITU
“Treatment of DCIS is less complex than treatment of invasive breast cancer,” said Dr Ow.
The mainstay is surgery, which can include lumpectomy (removal of the breast tumour) or mastectomy (removal of the whole breast). Dr Ng said the aim is to remove the DCIS and obtain “clear margins”, which means having no cancer cells present at the outer edge of the removed tissue.
In the case of a lumpectomy, radiotherapy would be required to treat the rest of the breast tissues after surgery, added Dr Ow.
Oncoplastic breast surgery with radiotherapy is also a good option, said Dr Ng. This method combines breast cancer surgery with plastic surgery techniques, to remove the tumour while preserving the natural contours of the breast.
And as DCIS is confined to the breast, localised treatments such as surgery and radiotherapy, are sufficient in addressing the problem, said Dr Ong. “This translates to an excellent cure rate after surgery without the need for harsh treatment, such as chemotherapy.”
While the likelihood of DCIS recurrence is very low, at four to eight per cent at 10 years, it does not mean that it will never recur, said Dr Ow. It can happen in the same breast or the other breast, he added.
While DCIS recurs far less frequently than invasive breast cancer, when it does recur, half the incidence rates are where the cancer has become invasive, said Dr Ong.
LIFESTYLE CHANGES TO REDUCE YOUR RISK
Like any cancer, DCIS cannot be completely prevented. However, lifestyle changes may reduce one’s risk.
“Prevention of DCIS is essentially the same as prevention of breast cancer,” said Dr Ow.
Simple things you can do include maintaining a healthy body weight, particularly for menopausal women, avoiding prolonged ingestion of hormone replacement, as well as abstaining from smoking and alcohol.
“Increased physical activity, having a child at a younger age and breastfeeding have also been found to reduce one’s risk of breast cancer,” added Dr Ow.
Ultimately, early detection is key. “A diagnosis at Stage 0 often means minimal interruption to [your life] and excellent survival outcomes,” said Dr Ng.
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