It seems particularly unfair for Callaghan to be taken from her loved ones so early.
There is an extra layer of hurt with her loss – the delay it took between the discovery of the lump last June and scans last November showing cancer also in other parts of the body.
Spend any time in the oncology area of a general hospital and you will come across people of a wide range of ages and backgrounds also battling the odds. Not unlike Covid-19 coronavirus victims, cancer sufferers tend to be middle-aged or older but people in their 20s and 30s can still get it.
Finding a possible tumour turns a person's life upside down in an instant.
Even then, it can take a while for the gravity of the situation to really sink in and to totally comprehend the implications of the medical information being absorbed. That is partly because the patient is usually a novice in the health environment they are suddenly thrust into.
And in the case of breast cancer, the signs of the problem may not be obvious – a person can have a dangerous tumour and yet feel normal.
A person's age, family medical history and own past health play a part in their likelihood of getting cancer. There are various known risk factors such as being overweight and having dietary, alcohol or exercise issues.
Callaghan's generally healthy lifestyle reportedly may have been a factor in the time lag.
Going through cancer treatment or watching a family member or friend experience it is like opening a door to a room that you knew existed but were unfamiliar with and previously felt you could ignore.
It is human nature to only learn from disasters and crises the hard way. People can be advised to take preventative measures if they have risk factors and they may even think they are listening and making changes.
Yet actually facing mortality brings a harsh clarity like nothing else to what is important in life and what needs to be done to stay alive, should you escape the immediate danger.
If people could somehow get an alert in advance on their future health, there are lessons to be found in the cancer room.
Acting quickly on any suspicious medical problem, and getting thorough medical advice and tests as soon as possible is essential. Delayed diagnoses are not uncommon. Catching a tumour before it spreads is important.
A mixture of a determined outlook and caution is the best approach to treatment. The patient needs to stay positive but not be too stoic and brush off symptoms that medical staff need to be told about.
Manage your risks before the worst happens because people can be left with ongoing problems after treatment and their immunity can be weakened.
And, as with the coronavirus, younger people should know that they can, like Kate Callaghan, be hit in a devastating way by cancer out of the blue and far too early.