The two organisations announced last month that they would formally combine on 1 April, forming a new charity with an annual income of more than £45m.
Both charities will initially operate as separate brands, with a new logo and name expected within a year of the merger.
The charities might have very similar names but their focus is very different: Breast Cancer Now funds research into the disease, but Breast Cancer Care focuses on supporting people with breast cancer diagnoses.
But many questions remain about what the merger will mean in the longer term for both organisations.
The staffing question
Breast Cancer Now currently employs 156 people and Breast Cancer Care has 205 employees.
The charities have already confirmed that Baroness Delyth Morgan, chief executive of Breast Cancer Now, will become the new organisation’s chief executive, with Samia al Qadhi, who has led Breast Cancer Care since 1994, stepping down on 31 March.
But one area of concern is whether the merger will lead to redundancies.
In 2015, Breast Cancer Now was formed by the merger of Breakthrough Breast Cancer and the Breast Cancer Campaign.
It lost about a quarter of its staff in a bid to remove duplicate job roles at the charity once the merger was completed.
Asked if the merger of Breast Cancer Now and Breast Cancer Care would lead to any redundancies or job losses, Morgan tells Third Sector that the "merger is not about a need for efficiencies" but is ultimately about growing impact.
"Therefore, every effort will be made to minimise redundancies and maximise retention," she says. "Retaining the combined talent and expertise across both charities is absolutely critical to the new charity’s future success."
Under the terms of the merger, Breast Cancer Care’s staff will transfer to Breast Cancer Now under the Tupe regulations. However, the merger will lead ultimately to the creation of a new identity for the combined charity.
Staff who transfer will keep all of their contractual terms and continuity of service benefits such as salary, holiday entitlement and sick pay, says Morgan.
"The boards of trustees of both organisations took independent advice on how best to legally and financially structure the new charity, and considered several options," says Morgan.
"The advice was that Breast Cancer Care should transfer into Breast Cancer Now, because Breast Cancer Now has a more complex financial structure for its research grants, and it would therefore be the more efficient way to merge the two existing legal entities."
Where will the combined charity be based?
The charities will move into Breast Cancer Now’s London base near Aldgate because Breast Cancer Care’s offices are too small, Morgan says.
Offices operated by Breast Cancer Care in Glasgow, Sheffield and Cardiff and by Breast Cancer Now in Edinburgh will remain unaffected, at least in the short to medium term, she says.
"The new charity will remain as committed as ever to the presence of both charities in the regions and nations," she says.
What will happen to the trustee board?
The charities have already announced that the combined charity will be chaired by Jill Thompson, who is currently treasurer of Breast Cancer Care. The new board will consist of six trustees from each of the two charities, and at least one-third of the trustees will have personal experience of breast cancer.
Both charities have been at pains to say the merger has not been driven by financial pressures, and their accounts appear to back that up.
Breast Cancer Now had an income of £28.3m and reserves of £10.7m in the year to 31 July 2017.
Breast Cancer Care had an income of £16.2m and reserves of £7.6m in the financial year to March 2018.
Levels of spending seemed within an acceptable level. Breast Cancer Now spent £29.9m in 2016/17 and Breast Cancer Care spent £16.4m in 2017/18. However, Breast Cancer Now says in its latest accounts that it is intending to reduce net expenditure.
What will be the impact on beneficiaries?
Morgan says that merging the two charities is "undeniably the right thing to do for those affected by breast cancer" and the merger will make a "lasting difference to the millions affected by this devastating disease".
She adds: "With incidences rising, inequalities in care remaining and more than 11,000 families torn apart by metastatic breast cancer every year in the UK, we need to do much, much more – and it is only together that we will be able to rise to this significant challenge."
What does this mean for the charity sector?
Some large charities have probably been put off the idea of a merger because of the difficulties of bringing together two complex organisations.
But Andrew Studd, a partner at the law firm Russell-Cooke, who worked on the merger, says these two charities coming together should show the trustees of other charities how a merger can work. "It encourages trustees to focus on areas where collaboration is more constructive than competition, especially in areas such as fundraising," he says.
Many charities would benefit from mergers because they would reduce competition for funding and potentially reduce overhead costs, argues Studd.
Richard Litchfield, chief executive of the management consultancy Eastside Primetimers, says trustees tend to shy away from mergers because of difficult decisions about bringing together two boards and who to appoint as chief executive. But he suspects times are changing.
Eastside Primetimers' annual Good Merger Index listed 54 mergers in 2015/16 and 70 in 2016/17. In 2017/18, the figure rose to 80.
"There's a definite upward trend, albeit from a low base," says Litchfield. "Merger is very much on boards' minds."