I’m so sorry about your sister - it’s really hard to hear news like this, but it’s important to try not to panic as the full picture when all tests are in may be very different from your fears.
Stage 4 cancer is metastatic - has spread to other organs or areas of the body. It’s generally referred to as treatable rather than curable and treatments focus on controlling the symptoms, slowing the progress of the disease and extending and improving quality of life. A breast cancer that is metastatic at initial diagnosis is called a DeNovo cancer. The treatments for these kinds of cancers have vastly improved over the last ten years, people are living a lot longer and with much improved quality of life. Treatments are tailored to the type of cancer, extent of spread and the general overall health, so will vary from person to person. There is also something called Oligometastatic breast cancer which has spread to just one area, or a very limited number of areas, and there are different targeted therapies for these.
When l was diagnosed with BC, last year, the type was lobular, which typically doesn’t present with lumps or bumps, and it was picked up at a routine mammogram. These tumours are difficult to see on scans so are usually large by the time they are discovered. Mine was a large tumour - 13cm at diagnosis -and despite it being described as a stage 1-2 cancer initially, l was advised to have MRI and CT investigation to ensure that none had broken away and spread undetected. Thankfully the scans were clear for distant spread, but at mastectomy it was found in the lymph nodes so they were removed to stop further spread, and the cancer was redefined as stage 3. The cancer l had was ‘cured’ by a combination of mastectomy, radiotherapy and l’ll be on hormone therapy for the next 8-10 years.
Hopefully OP, as well as your sister will find that once all the test results are in and there is a treatment plan, the outlook is not what they feared. I do hope so.
I think the OP has underscored the importance of being vigilant. Not all breast cancer presents with lumps or bumps, and it’s important to know other visible signs like ‘orange peel skin’, which appears as cancer cells block the lymphatic cells, causing a dimpled effect on the skin of the breast close to the tumour - it resembles orange peel in appearance. This was the only sign l had that there was a cancer and unfortunately l didn’t recognise it.
There are other visible signs that something may be wrong and it’s important get them checked out no matter how insignificant you feel they are. Flushing or redness in the skin, or a thickened/hardened skin. Any visible swelling of the breast or a change in size or shape causing asymmetry. Nipple changes - inverted nipples which are not normal for you, any discharge or bleeding, or rash around the nipple area. Pain that doesn’t go away in the breast or armpit, and swelling of lymph nodes in the armpit or near the collarbone. Self examination is important and you can get advice from your GP or practice nurse on how to do it properly, but it should be combined with looking for any visible signs. And despite the discomfort involved, always attend for routine mammograms when you’re called. I would never have known my cancer was there if not for the mammogram, and had l missed it, l’d be telling a very different story now.