Start here

This is where you should start if you are newly diagnosed with a HER2-positive T1a (or T1mic or T1b) breast cancer tumor. Should you take chemotherapy and trastuzumab (Herceptin)?

If you already know about these “very small” sized tumors and the various biomarkers, including HER2, and if you simply want links to some of the most cited studies, trials, interviews, articles, and editorials, and the newest research, please see the Resources page.

If you need some background, this page will cover basic information about a T1a, T1b (and T1mic), HER2-positive diagnosis. Since globally accepted guidelines on the treatment of HER2-positive breast cancer go by size, we’ll start there.


Size is one component to determine the “stage” of cancer. Stages go from 0 to 4.

Breast cancer tumors in Stage 1 range in from 1 millimeter to 2 centimeters. Sizes are further broken into three groups: T1a, T1b, and T1c.

The graphic below is a visual aid. It’s sized for a computer screen, but it is to scale for all devices:

stage 1 sizing

(Note, size is only one factor in staging. Go here for a full understanding of how breast cancer is “staged”.)

There also is a size called “Tmic” that is not pictured. This categorization refers to microinvasion from ductal carcinoma in situ, or DCIS.

As DCIS, these cancer cells were contained in a duct. Tmic is somewhere between DCIS and invasive cancer. Tmic cancer cells have broke through the membrane of the duct, but in very small numbers.

The DCIS lesion with microinvasion could be large, but if the cancer cells are not seen invading through the duct, it is DCIS. If the invasion is more significant, it is invasive cancer.

Doctors call Tmic and T1a cases “medically interesting” because these cases are rare. If T1a cases are one in a hundred, consider Tmic cases as one in a thousand, relatively speaking.


Neoadjuvant therapy refers to treatment before the main treatment. For example, drugs to shrink a tumor before surgery would be neoadjuvant therapy.

Adjuvant therapies are the main treatment to remove or kill cancer cells and try to prevent the cancer from coming back. These treatments can be surgery, radiation, chemotherapy, and other drugs.

In the case of HER2-positive breast cancer, a drug called trastuzumab (marketed as Herceptin) is almost always given in conjunction with chemotherapy. What cocktail of drugs will be recommended for a patient depends, in part, on the size of the tumor and if the cancer has spread to the lymphatic or vascular systems.


Globally accepted guidelines by the the National Comprehensive Cancer Network (NCCN) say to “consider” chemotherapy and trastuzumab for HER2-positive tumors under 1 centimeter.

The graphic below illustrates the NCCN’s sizing guidelines. The images are sized for a computer screen, but are to scale on all devices. (Because it is so small, the .5 millimeter size is highlighted.)

NCCN HER2-positive guidelines

Many U.S. oncologists will recommend chemo and Herceptin for these “very small” tumors larger than half a centimeter. Is that over treatment? What about taking a less-intense regimen of chemotherapy? What about taking trastuzumab for a time period shorter than one year? These methods may reduce toxicity for patients, and these approaches currently are being studied.

Outside the U.S., it’s possible Herceptin will be prescribed without chemotherapy. How effective is that to lower recurrence risk? It’s not clear from existing evidence, as all studies focus on larger tumors – cases where chemotherapy is needed. Also, outside the U.S., sometimes trastuzumab is prescribed in subcutaneous form. An application for subcutaneous Herceptin in the U.S. is currently under consideration by the FDA. (News release is here.)


Tumor biology is important. No two cancers are the same, and biomarkers help determine a personalized treatment plan.

These are really complicated concepts, and I’m not a doctor or pathologist. I will generalize and highlight as a laywoman:

ER/PR-positive, or HR+: Hormone positive cancers mean estrogen and progesterone are accelerating growth. There are drugs like tamoxifen that block the hormones from sending signals to the cancer to grow faster, which can either slow or stop growth.

Grade: This is how abnormal the cancer cells look under the microscope. The higher the grade, the more aggressive the cancer is. Grade 1 cells are slightly abnormal. Grade 2 cells look more abnormal and grow faster than grade 1. Grade 3 cancer cells look really abnormal and grow very fast. Usually, but not always, HER2-positive cancer cells are not in the grade 1 category.

Ki67/Ki-67: This is the proliferation rate, or the rate at which cancer cells reproduce. There is no universal “division line” or “cut off point” on measuring slow versus fast growth. Some researchers believe under 10 percent is low, 11 to 20 percent is intermediate, and over 20 percent is fast growth. Others believe under 14 percent is low to intermediate, while over 14 percent is fast. (This is biomarker seems to be getting a lot of recent attention.)

HER2/CEP 17 ratio: This is the rate at which HER2-positive cancer cells make protein for division and growth. This ratio is usually identified on something called a FISH test that sometimes can supplement a basic pathology report. Anything equal to or greater than 2.0 is positive for HER2.

For much more information on these biomarkers and others, please, speak to your doctor in relation to your own pathology report. These biomarkers are important. Variations on my own biomarkers helped me make decisions about my own adjuvant treatment.

If you don’t know how to read a pathology report, has an easy-to-understand guide. Find that here. You will also find many more helpful links on the Resources page.

Other considerations will come into play on your treatment plan as well, such as your menopausal status, whether you’ve had children, your family history, and other factors. No two cancers are alike – just as no two patients are alike. Make sure you understand everything about your case.


The information contained in this blog is not intended to be used for medical diagnosis or treatment. It should not be used in place of the advice of your doctor or other qualified health care provider.