Are all pathology reports hard to comprehend?

Some pathology reports are quite confusing, others less so. 

There are very specific pathololgy terms and handbooks upon handbooks that explain how something that looks like "X" should be described, as opposed to something that looks like "x".  Pathologists should - and usually do - use the correct medical / pathology terminology to describe what they see under the microscope. Pathologists are doctors, and then beyond that they have specialty training in pathology.  They spending years learning how to identify what they see and how to describe it properly.  

In other words, they spend years learning how to describe something in a way that might be confusing to a layperson!  And that's why we so often find pathology reports to be confusing. 

The issue about getting a second opinion relates more to the fact that pathology is not always a precise science.  When looking at these tiny tiny cells under a microscope, what one pathologists sees as being one thing might be seen by another pathologist as being something else.  When there are large amounts of tissue to examine, usually this isn't a problem. But when searching for something that represent an area of invasion, something that might be a fraction of a millimeter in size, hidden in the middle of a larger amount of DCIS, it's possible to get two different opinions from two pathologists looking at the same slides. It really is like looking for a needle in a haystack. So if you do have questions or uncertainties about your pathology, getting a second look at the slides is a good idea.

As for why the pathologist didn't rule out invasion with "other more rigorous tests", that's because there aren't any other more rigorous tests. 

By the way, as a layperson, I interpret your pathologist report as saying there is no invasion.  What was identified were a few tiny areas ("a few small foci" - this probably means fractions of a mm in size) that appear to be edging toward invasion but those areas remain contained within the duct and therefore are still DCIS.  

Deb, you didn't include a link to the article that you referenced that mentions these two different definitions of microinvasion but I think I found it.  Is this it?  http://www.aboutcancer.com/breast_dcis_harris.htm  It appears that this article is from 1997 and the good news is that there has been more clarity in the definition since then.  

"DCIS with microinvasion (DCISM) was defined in 2003 by the American Joint Committee on Cancer as “the extension of cancer cells beyond the basement membrane into the adjacent tissues, with no single focus larger than 1 mm in greatest dimension (T1mic)”" http://jnci.oxfordjournals.org/content/96/12/906.full

"The definition of microinvasion in breast carcinoma has been controversial, being lumped together with "minimally invasive breast cancer", defined as "a few high power fields" in extent or arbitrarily designated as invasion not more than 2 mm from the basement membrane of the adjacent in situ component. It has also been defined as a single focus of invasion not more than 2 mm in extent, or up to 3 foci, each measuring not more than 1 mm. Microinvasion is a lesion that is almost always associated with extensive DCIS. The currently accepted definition as adopted by the TNM system (T1mic) clarifies it as cancer cells extending beyond the basement membrane into adjacent tissues with no focus larger than 1 mm, using only the largest focus for classification. This criterion is also recommended in the United Kingdom breast screening pathology guidelines, which also adds the caveat that the invasive focus should enter the interlobular stroma."  http://www.annals.edu.sg/cpd1101.html

Here is the 2003 AJC definition, taken from their breast cancer staging (TMN classification) manual: "Microinvasion is the extension of cancer cells beyond the baseline membrane into the adjacent tissues with no focus more than 0.1 cm in greatest dimension.  When there are multiple foci of microinvasion, the size of only the largest focus is used to classify the microinvasion.  (Do not use the sum of all the individual foci.) The presence of multiple foci of microinvasion should be noted and/or quantified, as it is with multiple larger invasive carcinomas."  http://www.cancerstaging.org/products/csmanual6ed-4.pdf

All that said, it's true that there remain questions about how a microinvasion is defined. But what's important to consider is that this doesn't (or shouldn't) change what a pathologist sees under the microscope or how the pathologist describes in writing on the pathology report what he or she saw. Questions about the defintion of a microinvasion would change only the label that's put on it at the end.

Good luck with your second opinion.  I hope that it provides you with the clarity that you are looking for, and I hope that that it agrees with your first opinion. When I was going through this, I found that having 2 opinions that were consistent was the best way to feel comfortable!