[Aussie Girl]

Dear Andi,

I'm an Australian pathologist who managed to grow her own HER2+ cancer, although not lobular carcinoma.

I don't think I have ever seen a HER2+ lobular carcinoma, but I have seen one reference indicating that it occurs at a rate of roughly 5% of HER2 cancers. That makes your cancer maybe 1 in a 100.

I don't know what pathological criteria were used for determining the cancer subtypes in order to get the 5% figure.

When your carcinoma was detected in 1995, determination of the type of cancer was based only on what it looked like under the microscope on routine stains. There is, it has been discovered, an overlap between what a lobular and a duct carcinoma look like - one can mimic the other and vice versa. Some cancers can have both lobular and ductal components in the one lesion.

Subsequently a new test to check if a cancer is lobular or ductal was introduced. It is called an E-cadherin stain which is performed on fresh cut slides of the original tumor. It would be very interesting for your doctors to check if your original tumor was E-cadherin negative, as would be expected for a lobular carcinoma. A ductal carcinoma would show positive membrane staining.

Also in some cases, HER2 positivity is "heterogeneous" which means "mixed". This means part of the tumor shows amplification and part is negative. Usually in a mixed lobular and ductal carcinoma it would be the ductal carcinoma which was HER2 positive.

I would expect there would be no difference is therapy whatever carcinoma subtype you had. It's the ER and HER2 status, tumor size, grade and extent of spread which are important.

Cheers and glad your recent biopsy turned out to be OK.
Aussie Girl