LCIS - rare???

I don't understand how they know LCIS is so rare. I guess they are basing it on the number of breast surgeries that contain LCIS. But that wouldn't tell for sure when you have a lumpectomy. ( could be in other breast or another part of lumpectomy breast) So maybe it's just double mastectomies.

They don't know that LCIS is rare. To be diagnosed with LCIS (or almost any invasive breast cancer), they need to look at a piece of tissue under the microscope. They don't know how many men or women are walking around with LCIS and have never had any of their breast tissue looked at under a microscope. It is impossible to tell for sure that you have excluded a diagnosis of LCIS, even from double mastectomies, because when they make specimen slides from breast tissue, they do not look at EVERY cell in the mastectomy. Plus, a mastectomy does not remove EVERY breast cell.

They DO know the (approximate) number of patients get diagnosed with LCIS from biopsies or mastectomies, and in that group, LCIS is an unusual diagnosis.

They also say that most LCIS doesn't become cancerous. Well, how do they know that?

They can look at the people who have had LCIS, and see whether or not they end up getting breast cancer in their lifetimes. While some breast cancers can recur over 50 years after their first occurrence https://www.ncbi.nlm.nih.gov/pubmed/22606439, this is very unusual. (Most people get diagnosed with LCIS in their 40s or 50s.) Its almost impossible to study LCIS and if/when it becomes cancerous.

I don't think LCIS shows up on imaging - does it?

LCIS cannot be diagnosed without looking at a piece of tissue under the microscope. Doctors don't take tissue out of a breast and look at it under the microscope without a reason to do so. Usually doctors are looking at a breast lump, or something suspicious seen on a mammogram or ultrasound or MRI or other imaging, or, perhaps someone is getting a breast reduction for cosmetic reasons, or getting a mastectomy because they have a horrible family history of breast/ovarian cancer. That said, sometimes LCIS is seen not AT the site of an abnormality, but adjacent to it. So, you're right, sometimes LCIS shows up in imaging, but sometimes it doesn't.

There are a lot of unknowns and controversy with LCIS. Its a weird condition. But, speaking for myself, I'd MUCH rather have plain LCIS (in other words only LCIS), rather than DCIS or an invasive breast cancer.

Well, LCIS is very hard to study. We can't look at a spot of LCIS in a breast and monitor it over time, because you can't tell that its LCIS unless you look at the tissue under the microscope, which, of course, involves removal or at least a disturbance of the area.

They do know that when classic LCIS women go on later to get invasive breast cancer, the area that the invasive breast cancer grows sometimes/often previously looked normal under imaging.

In this paper, they state These data, further strengthened by the molecular data discussed above, support LCIS being both a nonobligate precursor and a marker for increased risk of developing invasive carcinoma. https://www.archivesofpathology.org/doi/10.5858/ar...:rid:crossref.org&rfr_dat=cr_pub%3dpubmed A nonobligate precursor means that sometimes an LCIS area actually turns into invasive breast cancer. A marker for increased risk of developing invasive carcinoma means that if you find LCIS anywhere in a breast, the entire breast is at increased risk of breast cancer. When LCIS people later get invasive breast cancer, sometimes the invasive breast cancer is genetically related to the previous LCIS, but in other patients, or in other breast cancers in the same patient, the invasive cancer isn't genetically related to their previous LCIS.

So LCIS people are more likely to get invasive lobular carcinoma than the general population (presumably these are cases where LCIS developed into invasive lobular carcinoma), but still most LCIS women go on to get invasive ductal carcinoma (like the general population), thus a sizable number of LCIS patients get cancers that are less genetically related to their LCIS. (Roughly 80% of the general population of invasive breast cancer patients get invasive ductal carcinoma, whereas in LCIS patients its more like ROUGHLY 60% ductal. These numbers vary quite a bit from study to study.) Since LCIS is less genetically related to invasive ductal carcinoma than invasive lobular carcinoma, presumably more of these IDC cases are due to the LCIS acting like a risk factor.

Because LCIS can act like a risk factor for the entire breast, just removing the known areas of LCIS won't eliminate all of the increased risk. I suppose theoretically it might reduce the chance of that spot of LCIS genetically developing into an invasive breast cancer, but since most LCIS people have multiple spots of LCIS, and often in both breasts, and many/all of these LCIS spots are undetectable, you can't remove all the LCIS in a breast, except perhaps in a mastectomy. (Even a mastectomy doesn't remove all breast tissue.) Obtaining negative surgical margins in excision specimens for classic LCIS is not necessary or recommended. https://www.archivesofpathology.org/doi/10.5858/ar...:rid:crossref.org&rfr_dat=cr_pub%3dpubmed

On the other hand, if you have florid or pleomorphic LCIS, then those types are thought to be more aggressive. Since florid and pleomorphic LCIS is less common than classic LCIS, they know even less about them.

Hope this gives you an idea about the uncertainty and controversy concerning LCIS treatment. I've seen papers that recommend that if a person has both an invasive breast cancer and LCIS, if the invasive breast cancer is treated normally, they don't have any worse outcome than people who 'just' have a comparable invasive breast cancer. But I'm sure those opinions are controversial too.

Best wishes.

I had a core biopsy 8 years ago based on suspicious mammogram findings. It came back positive for LCIS. They then did a lumpectomy to remove it. At the time they told me (my words eight years later from what I recall), that my chances of getting cancer in 8-10 years was significantly increased in both breasts. Here we are 8 years later and I now have invasive Lobular Carcinoma. My guess in saying it is rare is that 80 percent of breast cancers are ductal. Lobular make up only about 10% (that number varies by site). The good thing about it is they step up monitoring if you have LCIS. I went to every 6 months, alternating mammograms with MRIs and Ultrasounds, so my cancer was caught early. Mine was on the same side, however I opted for a double mastectomy since of increased odds with LCIS, ADH, ALH, Dense tissue plus family history. The Pathology report showed I had LCIS in the opposite side as well, so I am happy I chose the path I did.