The math of invasive breast cancer risk for LCIS

Posted by elsie37 @elsie37, Mar 30, 2019

Lobular Cacrinoma in Situ (LCIS) confers a risk of invasive breast cancer of about 2% a year, maybe a little less, when chemoprovention endocrine meds are NOT taken. If meds are taken, the risk is cut in about half, maybe even cut a little more, so 1% or less.

Furthermore, LCIS is a lifetime risk. That means any 40 year old woman diagnosed with LCIS who could expect to live until 85 has a lifetime risk of 2%/year x 45 more years of life = 90% lifetime risk of cancer. Let's say the risk is only 1.5% per year, to be wildly optimistic and not 2%, since some studies have indicated the annual risk is less than 2%. Then that comes out to a 67.5% lifetime risk, still a big number. (1.5%/year x 45 more years of life)

Other sources show a lifetime risk of developing invasive breast cancer with LCIS to be 20% with some showing up to 35%. Those results do not come out to 2%/year for most women, unless the diagnosis is made at around 65 years or older.

Examples: Age 65 at diagnosis with life expectancy of 85 years means if using even the lower 1.5%/year risk, it is 1.5%/year x 20 more years of life = 30% lifetime risk. Age 70 at diagnosis with life expectancy of 85 years, again using the 1.5% figure is 1.5%/year x 15 more years = 22.5% lifetime risk.

Even the halved annual risk of 1% over a lifetime that may be obtained by taking chemoprovention endocrine meds still does not add up to a halved 10%-18% (instead of 20%- 35%) life time risk of invasive breast cancer,

Example: LCIS diagnosis at age 40 with life expectancy of 85. 1%/year x 45 years to reach age 85 = 45% lifetime risk. While better than even odds for a 40-year old, I think many women would consider something that close to 50% of getting cancer to be too high, especially after investing 5-10+ years of taking risk-reducing drugs, which produce substantial side effects for many. But a diagnosis at age 55 with a 1% annual risk due to medications, would result in a 30% lifetime risk, if life expectancy was 85. (1%/year x 30 years = 30%)

Interestingly, I have repeatedly seen that of all the LCIS diagnoses, only 10%-20% are in women past menopause, so using ages 55-75 for examples to make the annual risk come out similar as lifetime risk does not reflect the reality of who has the most cases of LCIS. I have also read that the number of post-menopause LCIS cases, though now a minority, is growing. And I am one.

Some of us have high hopes of making it to 90+ if we've had many relatives who have lived that long, so that means that 2%/year (or the more optimistic 1.5% or even the 1% with drugs) really makes lifetime risk soar upward.

For women diagnosed in their 30s, or younger, those 2%s accumulate over an even longer period, so that the odds of invasive cancer could easily reach 100% over a lifetime. Or more, but of course that is not possible. However, no studies I have found warn of guaranteed invasive breast cancer (100%) for those with LCIS if you live long enough.

Something does not add up. Perhaps it is the mathematician, (me). Or my LCIS assumptions are wrong. Maybe risk does not increase in a linear fashion year after year, maybe it tapers off? It seems to me that either all the lifetime risk numbers out there from reputable sources are wrong or the 2%/year over a lifetime (halved or more with medication) is wrong. So that those of us with LCIS can decide what treatment is best, we need to know which numbers are right–and which are wrong.

Can the Mayo experts or the moderator or another poster shed some light? Thank you in advance.

Interested in more discussions like this? Go to the Breast Cancer group.


Nothing correlates as far as I can see. They all seem to recommend cancer preventing drugs which come with its own set of risks. For me I was researching after a year of hell of waiting for biopsy results. One woman on a fb group page wrote. “Would you get on a plane if it had a 20 percent chance of going down.” Granted that is not a great example. I personally have lost trust in the system. For years I felt that I was doing everything so that I can catch something in time unlike many of my family members that have passed. My family tree is so sad. Never in my wildest dreams did I expect for a doctor to tell me that they have a hard time seeing lobular since it forms lines similar to those in normal imaging. I became angry. I hope and pray my pathology comes back ok. What I am doing tomorrow is making me feel in more in control than I have felt in years. I pray for all of us those who have gotten sick from implants and just anyone touched in any way by cancer because it affects everyone involved. I am so sorry you are thinking of all of this also. It is not fair and upsetting. Please message I will be happy to talk or exchange thoughts about the process I am going through or anything. Good luck ❤️

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With all of the research on breast cancer you thin we'd know more. LCIS is rare, from what I understand


Mucusious carcinoma…you are the second person that I know that seems to be aware of that. None of the doctors I have talked to…I am on my 3rd oncologist this time around….had a clue what I was talking about. The other person that is aware of it is my brother. He had it in 2018…it was in a tear duct or something by his eye. I had BC for the second time when he was going through this and he told his doctor and the Dr told him to tell me because there is a connection with BC that I should have genetic testing. I did get the testing and have the CHEK2 mutation which involved with BC. Anyway, since no one else has said anything about it, could you share some of your information about? I did not have mutinous carcinoma…IDC though. My brother has to go yearly for a mammogram.

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Hello so sorry to hear that your brother has this type of cancer. I can tell you my cancer and those of my sons were reacted by Duke as an environmental exposure. our nightmare begin at Ft McCellan Ala – adjacent to the Monsanto properties.
This type of cancer is very rare and spreads through the mucous membranes in your body.
This is what the literature I have researched
Tells me. If your brother or your parents -grandparents were ever in the military and stationed at several bases it has been determined to pass generations. 5 decades were studied and rare cancers and other autoimmune diseases have been added to the list. A web site you may want to look at is ( there have been useful links there. My oncology team are excellent
I first went to Duke Hospital where they did genetics and multiple layer testing. There was no cancer in family link. It started with my spouse and me. We had 4 children. My spouse had GBD and is deceased. Both sons passed with in a year of each other. Renal Cell and leomeysarcoma. Both daughters are ill. One had ductal carcinoma and ovarian. Mastectomy bilateral and total hysterectomy.
Now in remission however also has autoimmune diseases. The other daughter has unspecified lumps in breast and autoimmune diseases. She is being studied to see what they can do.
The grandchildren are also affected. Granddaughter has RRMS. Recurring relapsing multiple sclerosis and it goes on and on. Research through government website and the above mentioned link.
God Bless


Wow. I cannot even imagine. So sorry for your losses and the pain your family is going through.


Thank you it is definitely a challenge that no one wants to face. However we are using it as a means to try and help others. It’s a day by day thing and takes a lot of processing to even begin to comprehend the big picture.


No one in my family had cancer until they were in their 70s. I did not test positive either. When I was 40 I had a ductile lavage after lumpectomy. They felt that I had 7 to 8 years of being clear. At that time they said I was 2 stages away from cancer. It was up to me take the Tamoxifen. I did not. 8 years later it was found on a MRI, 3 months after a mammogram at Stage 0. MRI Had caught it very early. I took Tamoxifen for 4 1/2 years until I had a black blood clot.

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Was your Stage 0 mammogram DCIS, LCIS, or some other diagnosis? Thanks.


Was your Stage 0 mammogram DCIS, LCIS, or some other diagnosis? Thanks.

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MRI, ductal

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