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Supermarket Card Surveillance Could Help to Spot Ovarian Cancer

Supermarket loyalty cards could do more than save people money – an innovative study funded by Cancer Research UK (CRUK) suggested that the data gathered could even help to save lives, by spotting early signs of cancer.

Results of the study, published in JMIR Public Health and Surveillance, showed that tracking purchases of over-the-counter (OTC) medicines, via loyalty-card data, could help to identify ovarian cancer symptoms sooner.

Researchers from Imperial College London, University College London and the University of Birmingham said that OTC medications are frequently used to self-care for nonspecific ovarian cancer symptoms prior to diagnosis. They reasoned that a significant change in purchasing behaviour, specifically an increase in self-medication prior to presentation in primary care, could be an indication of early signs of disease, and monitoring such purchases might therefore provide an opportunity for earlier diagnosis.

Medication Purchases Increase Before Diagnosis

A proof-of-concept study in 2019 suggested there might be a case for this, so the team initiated the Cancer Loyalty Card Study (CLOCS) to compare monthly purchases of OTC pain and indigestion medications prior to diagnosis in women with (n=153) and without (n=120) ovarian cancer, using loyalty card data from two UK-based high street retailers.

A majority of British shoppers are signed up to at least one loyalty card scheme. The women were all over 18, happy for their card data to be used, and agreed to complete a short questionnaire about ovarian cancer risk factors, along with any symptoms they had experienced and, for cases, the number of visits to their GP in the year leading up to cancer referral or diagnosis.

Cases were women recruited from 12 NHS clinic sites in England, Wales, and Scotland who had been diagnosed with ovarian cancer within 2 years of recruitment to the study, which ran from 1 November 2019 until 31 January 2022. Most (75.8%) had serous ovarian cancer and of those, 94% had been diagnosed at stage 3 or 4. Controls were recruited from various online and email sources. Cases were on average about 13 years older than controls; 47% of cases and 33% of controls owned cards from both retailers, while the remaining participants had one or the other.

After obtaining explicit consent, up to 6 years of loyalty card purchase history were requested from the two high street retailers. Participants with a previous cancer diagnosis were excluded, and cases were matched with controls by age and cardholder status. Among the final participants, only oral contraceptive use was associated with ovarian cancer risk, and was therefore the only risk factor adjusted for in subsequent purchase history analyses.

Increased Pain and Indigestion Medicine Use Among Cases

Throughout the 24 months of the study, card data showed an increased average cumulative number of purchases of pain and indigestion medications among cases before diagnosis compared with controls. The mean numbers of purchases of pain and indigestion medications were greater for cases in the 6 months, 12 months, and 24 months before diagnosis, with a significant association between purchases and diagnosis in the 6 months before diagnosis.

The rate of purchases of both types of medication bought together was increased among cases 8 months before diagnosis, at which time there was maximum discrimination between cases and controls (Fisher exact odds ratio [OR] 2.9, 95% CI 2.1-4.1). An increase in indigestion medication purchases was detected up to 9 months before diagnosis (adjusted conditional logistic regression OR 1.38, 95% CI 1.04-1.83).

When stratified by stage of diagnosis, among those diagnosed at an early stage, purchase of pain medications was identified at 15 months before diagnosis, whereas indigestion medications were much more closely associated to diagnosis, at 4 months. For those diagnosed at a late stage, indigestion medication purchases were identified as early as 13 months prior to diagnosis, and then in every month from 6 months up to diagnosis, but no significant change in pain medication purchases was found in the 12 months prior to diagnosis.

Unique Interval in Tumour Development

"From a clinical point of view, this highlights a unique interval in the tumour development where symptoms are presenting at different times," they said. However, the study was too small to further stratify according to patient characteristics based on their OTC use associated with reported symptoms and stage at diagnosis.

The researchers concluded: "There is a difference in purchases of pain and indigestion medications among women with and without ovarian cancer up to 8 months before diagnosis.

"Facilitating earlier presentation among those who self-care for symptoms using this novel data source could improve ovarian cancer patients' options for treatment and improve survival."

The team said that further studies with more patients, diagnosed at different stages, and more participating retailers, were needed to verify these findings. However, they ventured, this could "lead to the future development of an alert system for individuals to seek medical attention for the symptoms they are experiencing sooner than they might otherwise".

Further Studies in Other Types of Cancer

The team have received further funding from CRUK to continue their work by investigating whether purchases of OTC products could be used in a similar way to detect other cancers, such as stomach, liver, and bladder cancers, all of which also commonly have non-specific symptoms. 

Dr Yasemin Hirst of University College London, lead behavioural scientist on the study, said: "Self-care is an important part of recognising and managing the early signs and symptoms of cancer which could resemble common illnesses and can be cared for without the guidance from healthcare providers. It is therefore crucial to understand to what extent this process may influence timely presentation in healthcare."

She said that the CLOS project showed that "health behaviours can be measured beyond healthcare records, using transactional data. This data is very exciting for behavioural scientists to further explore life-style changes, dietary behaviours and perhaps exploring other datasets (e.g. biosensors) that can provide more information about self-care and health outcomes."

Lead author Dr James Flanagan, from Imperial College's Department of Surgery & Cancer, said: "The cancer symptoms we are looking for are very common, but for some women, they could be the first signs of something more serious."

The study "suggests that long before women have recognised their symptoms as alarming enough to go to the GP, they may be treating them at home".

Harnessing Data for Earlier Detection

Dr David Crosby, head of prevention and early detection research at CRUK, said: "Today, in the digital age, we live with a wealth of data at our fingertips. Studies like this are a great example of how we can harness this information for good and help us detect cancer earlier.

"It's incredible to think that this innovative study using loyalty cards, something most of us carry in our wallets, could help women with ovarian cancer, which is often diagnosed late and mimics the symptoms of other, more benign conditions.

"Whilst further research with more patients is needed, this study indicates exciting potential for a new way to detect cancer earlier and save lives."

Asked to comment on the study by Medscape News UK, Annwen Jones OBE, chief executive at Target Ovarian Cancer, said: "Finding ways to diagnose ovarian cancer at the earliest possible stage is vital to better outcomes. Two-thirds of women are diagnosed late, when the cancer is harder to treat, yet if diagnosed at the earliest stage, 9 in 10 women will survive.

"We find this study encouraging and look forward to hearing future updates following the undertaking of further research."

The idea for the study originated from an early detection innovation sandpit award run by CRUK, which was received in 2016. This sandpit initiative aims to drive forward the earlier detection of cancer. Following the sandpit award, the research was awarded an early detection project award to continue the work.