Would local recurrence be related to DCIS or invasive component?

There is no way to know.  However it's most likely that a recurrence would be caused by whatever cancer was closest to the margin.  So in your case, if you have a recurrence, because you had close margins on the DCIS but wide margins on the IDC, it's most likely that DCIS cells remained in your breast after surgery, on the other side of that close margin, and were not successfully killed off by the rads. And that's what would cause a recurrence.

But to your comment "My understanding is that local recurrence that stems from DCIS has a higher survival rate even if the recurrence is IDC than if the local recurrence stems from an invasive cancer", where did you hear that?  It's not something that I'ver ever heard.  Most IDC develops from DCIS, so I wouldn't have thought that there would be any difference whether an invasive local recurrence sourced directly from DCIS, or indirectly from DCIS (i.e. the cancer had evolved to be invasive prior to the first surgery).  If there is a study that you've read about this that suggests otherwise, I'd be really interested to read it.

Ah, but that's an apples and oranges comparison. 

If someone has pure DCIS, there is no risk of mets (or virtually no risk).  So if that individual then develops an invasive recurrence, because of that recurrence she now does face a risk of mets.  This means that if the mortality rate is 12% for women who have invasive recurrences after an initial diagnosis of DCIS, the entire 12% can be attributed to the recurrence. 

On the other hand, someone who had an original diagnosis that included invasive cancer would have faced a risk of mets right from the start. Then if she develops an invasive recurrence, she again is at risk of mets.  So if in the future she develops mets, there is no way to know if it sourced from the original diagnosis or from the recurrence. Therefore if the mortality rate is 35% for women with IDC who have a local recurrence, it's impossible to know how much of that 35% was caused by the original diagnosis and how much of it was caused by the recurrence.  However you have to consider that most women who develop mets never have a local recurrence; this suggests that even among those who do have a local recurrence, probably a large proportion of any cases of mets that develop later were caused by the original cancer, not by the local recurrence.  Further evidence of this are the dozens of studies that show that among those who have invasive cancer, mortality rates are virtually the same whether one has a lumpectomy or a mastectomy, even though local recurrence rates are higher for those who have a lumpectomy.  The mets is usually not caused by the recurrence.

In your case (as in mine, since I had a microinvasion too), the study that you provided doesn't apply because it refers to women who have a recurrence after an initial diagnosis of DCIS. But neither of us had a diagnosis of DCIS.  We had DCIS-Mi, which is Stage I because of that tiny amount of invasive cancer. So what's relevant to the mortality rate is not whether an invasive recurrence develops from DCIS cells or from IDC cells; what's relevant is whether the original diagnosis was pure DCIS (with no associated risk of mets) or whether there was some IDC present (with an associated risk of mets).

For anyone else reading who had pure DCIS and who might be scared by the mortality rates reported in the study and quoted here, keep in mind that these are the mortality rates among those who had an invasive recurrence.  In this study, of the women who had a MX for DCIS, only 0.5% had an invasive recurrence.  And of the women who had a lumpectomy for DCIS, 12% had an invasive recurrence.  So even among those who had a lumpectomy, the mortality rate was less than 2% (15% of the 12% who had an invasive recurrence).

I'm confused. I'm saying that the answer to your original question really doesn't matter.  If you have an invasive local recurrence, it doesn't make any difference at all if it sourced from the DCIS component of your original cancer or if it sourced from the invasive component of your original cancer.  Your odds of survival won't be any different in either case. 

If you are talking only about the mortality rate from the recurrence itself, not from the original cancer, then yes, that is what I'm saying.  A localized invasive recurrence is a localized invasive recurrence.  I don't see that it would make any difference if the recurrence sourced from DCIS cells or invasive cancer cells because you have no idea what happened behind the scenes.  If the recurrence sourced from DCIS cells, it means you probably had some pretty aggressive DCIS cells that converted to become invasive cancer and developed into a recurrence.  You don't know when those cells converted to become IDC - it could have been well before the local recurrence was discovered so they may have been sitting there for a long time, with lots of opportunity to move to the nodes or the bloodstream. Or upon converting, these formerly DCIS cells might be particularly aggressive (which is what led to the conversion to IDC in the first place) and therefore they might move quickly into the bloodstream or the nodes.  On the other hand, if the recurrence was caused by invasive cancer cells, those cells might been sitting dormant for a long time before forming into a small local recurrence. The IDC cells might not be particularly aggressive or inclined to travel, and maybe that's why they stuck around in the area of the breast and developed into a local recurrence, rather than go directly to mets.

Look at it this way:

Patient 1:  Original Diagnosis - Pure DCIS:                                  Risk of Mets 0%

.               Invasive Recurrence sourced from DCIS cells:             Risk of Mets 12%

Total Risk of Mets for this DCIS Patient after Invasive Recurrence:                   12%

.

Patient 2:  Original Diagnosis - DCIS-Mi:                                       Risk of Mets 2%

.              Invasive Recurrence (from either DCIS or IDC cells):     Risk of Mets 12%

Total Risk of Mets for this DCIS-Mi Patient with Invasive Recurrence:                14% 

.

Patient 3:  Original Diagnosis - Extensive IDC w/DCIS at margins: Risk of Mets  25%

.               Invasive Recurrence (from either DCIS or IDC cells):     Risk of Mets  12%

Total Risk of Mets for this IDC Patient with an Invasive Recurrence:                    37%

.

Those numbers are just examples but the point I'm trying to make is that the local invasive recurrence probably presents about the same risk in each case, and the same risk whether the recurrence sourced from DCIS cells or IDC cells.  The difference that you see in the studies of mortality rates between IDC patients who have an invasive recurrence and DCIS patients who have an invasive recurrence is due to the difference in the risk of mets that they face from the original diagnosis. 

By definition, a local recurrence happens when some stray cancer cells are left in the breast after surgery and are not subsequently killed off by rads or hormone therapy.  Over time (or immediately), those cancer cells start to multiply again and that's how a recurrence happens.

This means that if all of the cancer cells are removed or killed off, you can't have a local recurrence.  This is true whether the original cancer cells were DCIS or IDC.  In your case, because all of your invasive cancer was very far from the margins, the odds are extremely high that all those IDC cells were surgically removed and therefore you cannot develop a local recurrence that sources from that invasive cancer.  On the other hand, since your DCIS was right near the margins, the odds are greater that a few stray DCIS cells might be left around your breast area and if those cells were not killed off by rads, they could develop into a local recurrence. So in your case, I would speculate that a local recurrence is much more likely to be caused by the DCIS rather than the invasive cancer.  But if you did have a recurrence, looking at the cells themselves, I don't think there would be any way to actually confirm this.

The problem however is that the risk you face from the invasive cancer isn't gone just because all the cells were removed when you had surgery and therefore can't develop into a local invasive recurrence. That microinvasion came with another risk.  With any amount of invasive cancer, it's always possible that some of the cancer cells moved into the body prior to the surgery. If it was only a few cells, it's impossible to find them with any screening method.  But over time, these cells can develop into a distant recurrence.  So anyone with invasive cancer can develop a distant recurrence, i.e. mets, without ever having a local recurrence.  In fact, when mets develops, that's what happens most of the time. This means that your threat from that original invasive cancer isn't gone just because there is little to no risk of a local recurrence.

The other point I'm making is that you've made the assumption that "stray DCIS cells that have progressed" are a "relatively curable condition" whereas an "original invasive cancer (that) has a significantly higher probability of metastases".  What I am questioning is that assumption, as it relates to the development of a local recurrence and the risks from that recurrence.  DCIS cells that progress to become invasive are invasive cancer, just like any other invasive cancer.  They can be extremely aggressive, or they can be relatively indolent.  By the same token, those IDC cells that were in your original diagnosis started as DCIS cells, and there is no saying how aggressive, or indolent, they might be.  The only difference between the microinvasive IDC cells that were found in your original diagnosis, and any DCIS cells that might progress to become an invasive recurrence, is timing.  The timing of when the cell converted from DCIS to become invasive. 

For all you know, those microinvasive cells in your original diagnosis might have been DCIS cells just a month earlier, and for all you know, if some DCIS cells were left behind at the margins after your surgery, those cells could have progressed to become IDC a week after your surgery.  I'm not saying that would happen but I'm saying that it's possible and you just can't know.  In the end, both of those cells - the original microinvasive cells and the invasive recurrence - started as DCIS cells.  There is nothing that would suggest that one of those sets of cells would be any more or less aggressive, or curable, than the other.  The only significance of the timing difference is that the cells that were still DCIS at the time of your surgery did not have the opportunity, prior to surgery, to move into your nodes and bloodstream, whereas the cells that had already converted to become IDC did have a chance to do that (to the earlier discussion).  But if some DCIS cells were left in your breast after surgery and they then progressed to become invasive cancer, at that point the cancer is exactly the same as those original microinvasive cells, and they have the same ability to move to the nodes and into the bloodstream. Invasive cancer is invasive cancer.  Most of it started as DCIS, and some invasive cancers are highly aggressive and others are not.  The timing of when the cancer evolved from DCIS to become invasive doesn't affect the aggressiveness or curability.

Noquitter, THANK YOU!