About Carcinoma in Situ: Understanding the Two Types

In the breast, there are two types of carcinoma in situ: ductal carcinoma in situ (DCIS) and lobular carcinoma in situ (LCIS). In situ implies that the carcinoma cells have not yet escaped the confines of the ducts and lobules of the breast. (Once carcinoma cells leave the ducts and lobules and invade the surrounding breast tissues, it becomes invasive carcinoma).

LCIS & DCIS: Interrelated, yet distinct

Most DCIS arises in the larger ducts and LCIS arises within the lobules of the breast. However, the ducts and lobules are connected which means that DCIS may travel into the lobules and LCIS may travel up the ducts. For this reason, pathologists rely on the type of cells and pattern of growth to determine the diagnosis of DCIS vs. LCIS. Only a pathologist can make this distinction. In some cases, both DCIS and LCIS are present in the same biopsy.

DCIS and LCIS both increase a patient’s relative risk for developing invasive breast cancer and that risk applies to both breasts. However, DCIS is also thought to be a “precursor” to invasive carcinoma based upon numerous research studies. This is why your surgeon tries to remove all areas of DCIS from your breast and why many patients subsequently receive radiation therapy to that breast.

LCIS, on the other hand, has not traditionally been considered to be a “precursor” to invasive carcinoma, therefore complete removal of LCIS and radiation therapy is not required. There is emerging data that may change this way of thinking, but the current standard of care is to treat LCIS and DCIS differently. One exception to this may be pleomorphic LCIS which will be discussed later.

Ductal Carcinoma In Situ (DCIS)

DCIS is a complex diagnosis. If you are diagnosed, it’s important to know what grade of DCIS your pathologist has assigned (low, intermediate, or high), and whether or not necrosis (dead cells) are present.

If you have a diagnosis of DCIS on a core needle biopsy, you need to have a surgical procedure to try and remove all of the DCIS with adequate margins. If you have had a lumpectomy/partial mastectomy with a diagnosis of DCIS, be sure that the pathology report includes the following: the size of the DCIS, the grade, the presence or absence of necrosis, and the distance the DCIS is from the surgical margins. All of these factors influence what type of treatment you should receive next. Possible therapies include one or more of the following: additional surgery, radiation therapy, or endocrine therapy.

Lobular Carcinoma In Situ (LCIS)

Lobular carcinoma in situ (LCIS) refers to a neoplastic proliferation of cells that fill up the lobules in your breast and may extend into the duct system.

Unlike DCIS, LCIS is generally not graded by most pathologists. An exception is a recently described entity called “pleomorphic LCIS.” Pleomorphic LCIS refers to an in situ carcinoma with the characteristic features of LCIS, plus more atypical cells and often necrosis (dead cells). Pleomorphic LCIS can be difficult to distinguish from DCIS in many cases, but a special stain called e-cadherin can be used to help your pathologist make the distinction.

Treatment of LCIS vs. Pleomorphic LCIS

If you have a diagnosis of LCIS on a core needle biopsy, generally your surgeon will want to perform surgery to excise the area of concern, although this is somewhat controversial in the medical literature. If you have a diagnosis of only LCIS on your lumpectomy/partial mastectomy, there is no need to worry about clear margins and radiation therapy is not the standard of treatment. Unlike classic LCIS, there is no uniformly accepted standard treatment for pleomorphic LCIS, although many medical teams choose to treat it like DCIS.

Once you have a diagnosis of LCIS, because you are now at increased risk for developing invasive carcinoma, your medical team may recommend endocrine therapy.

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