"However, she listened to me when I said my breast looked different to usual and when I raised my arm I could see very, very feint [sic] dimples on the underside of my breast."
After going for a mammogram and ultrasound scan, Armstrong was told there was a tumour deep in her breast, close to the muscle.
"These three dimples have turned my world and my families world upside down," she explained.
"We are shocked, we are numb, we are emotional, we are sometimes ok, we are pretending it's not happening, we are trying to absorb information, we are dealing with tests, we are crying, we are trying to continue as normal.
"We are angry, we are sad. We have more questions than answers. We are doing our best to cope.
"The messages and phone calls to me, my husband and my children sometimes help and sometimes make us all cry."
She wrote: "I am sharing this because I hope I can make people aware that breast cancer is not always a detectable lump. Please go straight to your GP if you notice ANY change in your breast. It could save your life."
The Facebook post has been shared more than 100,000 times and many women have commented on the post, thanking Armstrong for sharing it.
One woman said it had even prompted her to go and get her breast checked. Gemma Webb wrote: "I have a very similar looking breast, its probably nothing but I've booked a doctor's appointment for tomorrow.
"I have a few other symptoms that I wouldn't have known about without seeing your photo and reading up on it.
"I've had three operations to remove pre cancerous cells from my cervix, and one to remove stage 1 cells. I'm currently awaiting biopsy results to see what's happening next, although I have a feeling inside it won't be the news I want.
"Thank you so much for sharing your photos and story. You're a beautiful, brave, admirable women."
Meanwhile Kristin Daniels shared her experience: "Kylie, I saw your post because one of my friends shared it. I, too, had the dimple, however I found a lump first, then noticed the dimple. That was 4 years ago. Thank you for posting this, it's so important for women to know ALL the changes that are BC signs."
She wrote: "We took the first major step in making me cancer free yesterday. I say 'we' because this affects everyone around me.
"My surgery went well and after a bit of early nausea, I am now recovering well. My family are tired but relieved this part is over. We hope all the cancer is now out of my body.
"Once I have fully recovered and my batteries have been recharged, we will jump head on to further treatment and we will do everything we can so I can beat this."
[Tap on the picture below to launch slideshow]
Breast Cancer Signs And Treatment
What Are The Symptoms?(01 of10)
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"A new painless, firm breast lump with irregular margins is a potential symptom of breast cancer," says Dr. Sandhya Pruthi, a breast cancer researcher at the Mayo Clinic. "The cancer diagnosis is confirmed following a biopsy of the lump." She notes that usually, women who are newly diagnosed with breast cancer are healthy and don't feel sick at all. (credit:LarsZahnerPhotography via Getty Images)
Other Symptoms(02 of10)
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Another potential symptom/sign of breast cancer, Pruthi notes, is a new onset of persistent redness on the skin overtop the breast with an orange peel appearance. This would also need a biopsy to confirm a diagnosis of breast cancer. (credit:Image Source via Getty Images)
Metastatic Cancer Symptoms(03 of10)
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"If the cancer is very advanced (metastatic) then the symptoms may also include weight loss, bone pain, headaches, nausea and persistent cough," Pruthi says. (credit:pamela burley via Getty Images)
What Are The Risk Factors?(04 of10)
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Some commonly associated risk factors, Pruthi says, are menstruation before age 11, menstruation after age 54, a first pregnancy after age 35 and a family history of relatives diagnosed with breast or ovarian cancer. (credit:AP Photo/M. Spencer Green)
Are There Any Lifestyle Risk Factors?(05 of10)
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"There is evidence in the literature that obesity after menopause, lack of regular exercise, consuming greater than more or more alcoholic beverages daily, and a high fat diet can all be associated with a higher breast cancer risk," Pruthi notes. But, she points out, "women need to know that any woman can get breast cancer even in the absence of any of these risk factors." (credit:Adrian Samson via Getty Images)
Can I Eat Anything To Prevent It?(06 of10)
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There are no specific types of diets, Pruthi says, but rather women are encouraged to eat fruits, vegetables, fibre, and minimize their alcohol and fat intake, as well as get regular exercise. (credit:lola1960 via Getty Images)
How Do Doctors Determine Treatment?(07 of10)
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"The most current treatment of breast cancer has taken on a individualized approach and is dependent on the biology or aggressive features of the breast cancer," Pruthi explains. "Breast cancer is a heterogeneous disease and this means that are many sub-types and different degrees of aggressiveness. So staging, which typically takes into account common prognostic features such as tumour size and if lymph nodes are involved, are no longer the only factors doctors use to determine treatment options." (credit:Christopher Futcher via Getty Images)
So What Do They Look At?(08 of10)
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"Today the biology of the tumour is also characterized by molecular markers (also known as predictive markers) such as if the estrogen or progesterone receptor is positive or negative and if the HER 2 protein is positive or negative," she says. "This helps decide who will benefit from a specific chemotherapy regimen, hormonal medications known as antiestrogens or who may need both chemotherapy and hormonal treatment." (credit:BluePlanetEarth via Getty Images)
What About Preventative Mastectomies?(09 of10)
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"Preventive mastectomy is an option for women at very high risk for developing breast cancer because they are BRCA 1 or 2 gene positive or if someone has hereditary predisposition to getting breast cancer but chooses not to have the genetic testing done," Pruthi says. "It is prudent that women who are considering this surgery know their family history in detail. Based on the moderate or strong family history, your doctor would recommend you meet with a genetic counselor to go over the family pedigree and help decide who should test for the breast cancer gene, when to test and how to interpret the genetic test results before proceeding with this preventive surgery." (credit:Jesús Jaime Mota via Getty Images)
Are Other Preventative Treatments Available?(10 of10)
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"High risk women who have had precancerous breast biopsies or strong family history may also be eligible to take preventive medications such as tamoxifen, raloxifene or exemestane to reduce breast cancer risk," Pruthi adds. (credit:art-4-art via Getty Images)