LCIS after microinvasive ductal carcinoma

If I read your post correctly, they found extensive LCIS and DCIS along with your microinvasive ductal carcinoma at your first diagnosis.

Now they found more LCIS (I assume classical LCIS.)

LCIS is normally multifocal (meaning it usually occurs in several different spots in the same breast), and it is often bilateral (meaning it often occurs in the other breast).  They know this because prior to the mid-1990s or so, bilateral mastectomy was a usual treatment for classical LCIS, and they found these multiple spots of LCIS in the mastectomy specimens. (They didn't 'discover' pleomorphic LCIS until the late 1990s/early 2000s.  We don't know if some of the pleomorphic LCIS prior to the late 1990s/early 2000s was misclassified as classic LCIS or as DCIS or something else.)

They don't know much about pleomorphic LCIS, but in classic LCIS, of the women who later go on to get invasive breast cancer, much of this invasive cancer occurs at a site that previously looked to be completely normal.  When they excise (plain, classic) LCIS, they often find LCIS not AT the lesion that prompted the biopsy, but ADJACENT to it.  LCIS is weird.  In a SMALL number of cases, they think LCIS itself may morph into invasive, but when classic LCIS morphs into something worse, MOST of the time they think it does NOT occur at the site of previous LCIS.  But those studies, of course, are not easy to do.  They are usually looking at chromosome mutation patterns.

Since LCIS is normally detected only at a biopsy, we can't tell what places in a breast have LCIS without biopsying it.   But it doesn't really matter because it puts both breasts at risk. 

They don't REQUIRE excision of all LCIS spots (unlike DCIS).  Since, unlike DCIS, they usually can't tell where LCIS occurs, they don't know where to excise, and if they excise everywhere, that's bilateral mastectomies, which in some ROUGHLY 60-80% of women, would be unneccessary. (Roughly 60-80% of women with LCIS and nothing worse will never go on to get bc.)

I am NOT trying to belittle the LCIS women who choose bilateral mastectomy.  It is a completely valid and recommended choice for many women.  I hope every woman with LCIS gets a choice as to their treatment.

Nevertheless, for plain, classic LCIS and nothing worse, they usually estimate the risk of breast cancer for a woman with classic LCIS and nothing worse (?excluding those with a significant family history) as ROUGHLY 0.5-1% per year. Since most classic LCIS women get diagnosed in their 40s or 50s, this means a representative lifetime risk of DCIS or worse may be ROUGHLY 20-40%  (assuming you live to be in your 80s.)

I can't find any published papers that look specifically at the treatment of 'newly discovered' LCIS AFTER treatment for breast cancer worse than LCIS.  But I would guess that it is likely the newly discovered LCIS was probably present when you got diagnosed with LCIS, DCIS, and microinvasive ductal carcinoma 4 years ago.

I had DCIS in a breast 10 years ago; had a lumpectomy without clear margins; and then had a mastectomy.  After AC chemo, I was on arimidex.  In December, I was diagnosed with LCIS in the other breast while on arimidex and had a second mastectomy where the surgeon found other areas as well.  Now on CMF chemo every 3 weeks for 6 months, after which I will be on tamoxifen.  Will have my ovaries removed after chemo, and then will get on with my life without worrying about mets!  Was surprised that one can have DCIS and LCIS in the same breast.