Is it possible to have 2 different types of tumors - same breast, same time?

DX 1/06 with IDC.  2 tumors in different quadrants, so mastectomy done 2/10/06.  First tumor IDC, well-differentiated, 2.4 cm, mod B-R/Nottingham grade I out of III (architectural score 1, nuclear score 1 to 2, mitotic score 1) with less than 10% DCIS component, cribriform, low to intermediate nuclear grade, ER+ PR+ HER2-.  Separate focus of IDC, moderately differentiated, 1.7 cm, mod B-R/Nottingham grade II out of III (architectural score 3, nuclear score 2, mitotic score 2) with approx 20% DCIS component, cribriform with focal luminal necrosis, intermediate nuclear grade, ER+ PR+ HER2+ with staining intensity 2.2 with IHC methodology (less than 2.0 considered negative).  26 axillary lymph nodes negative.  

How can I have one tumor that is HER2- and the other HER2+?  Given that I have no family history of BC, how likely is it that I have two totally different types of cancer occurring at the same time?  Should I request a FISH test to make sure the smaller tumor is HER2?  Is there a significant error rate on IHC testing compared to FISH?  Assuming HER2+, is there a test for Topo II available to determine if my tumor is responsive to anthracycline-based chemo?  I would prefer to avoid them if at all possible.

[CCF-RN,MSN-rf]

Dear paminlr:  It is technically possible for there to be two distinct breast cancers occurring at the same time.  For purposes of treatment, the most aggressive cancer would be considered.  In terms of the HER2, FISH technique is considered to be more accurate than IHC.  Since there is question, it may be valid to submit specimens from both tumors for FISH analysis.  While there may be laboratory testing for Topo II, it is not used as a basis for clinical decision making outside of a research setting.

[Twocapes]

I would definitely request having FISH done on the positive HER2 tumor.  Most path labs will automatically send it on if it is positive.  My IHC came back positive and the FISH came back negative, definitely helping with the decision of going on or not going on Herceptin.  I would also ask for a second pathology opinion.  Most path labs will forward them for you or you can get them and take or send them yourself.  Good luck - keep us posted.

[paminlr]

Thank you so much for the info.  I checked the path report and there is a notation after the statement that the test was performed by IHC that says "If Her-2/neu by other test modality (i.e. FISH) is required, please notify this office".  I called my surgeon and asked how to get the FISH test done.  He recommended an oncologist who returned my call and told me that he had seen several patients who were HER2+ by IHC test but negative by FISH.  I will be seeing him very soon.  What is most amazing (and upsetting) to me is that I previously saw 2 oncologists who never mentioned FISH to me or requested that it be done - both wanted me to take aggressive chemo and then herceptin for a year.  I only heard about FISH by my own research and even I know that herceptin won't me do a darn bit of good if the cancer is not HER2+.  I am so grateful for forums like this one and I am convinced that the internet is a necessary tool for cancer patients who want to be sure they have the most appropriate and therefore the best possible treatment plan.

[paminlr]

Thank you, Twocapes, you were right.  The FISH test was HER2-.  My new (third) oncologist told me that when he sees a HER2+ on an IHC test from the hospital where I had the mastectomy done, he almost always requests a FISH test.  He said that about half of them turn out to be false positives.  I plan to spread the word.  Right after my daughter and I finish doing our happy dance.

[Twocapes]

I just decided to scroll back and found your note.  I am so glad that the test turned out negative.  I wish there were some way to write directly to people who leave comments on this board as you may not get to see this.