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Breast Cancer

Breast cancer occurs when certain cells within the breast grow in an uncontrolled, abnormal, manner. Breast cancer forms in the ducts and tubes that carry milk to the nipple, and lobules, the glands that make milk. It occurs in both men and women, although male breast cancer is rare.

Sample Scan

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A) PEM identified cancer (large arrow), mass in posterior breast (small arrow), abnormal reroareolar uptake (arrowhead). B) Latter 2 lesions were not seen on whole-body PET.CT.

According to estimates by the American Cancer Society, more than 232,000 people in the United States will be diagnosed with breast cancer and nearly 40,000 people will die from the disease in 2011. Accurately pinpointing the location of the primary tumor(s) and determining whether the cancer has spread to other parts of the body are critical for determining treatment options for people with breast cancer.

Physicians are using molecular imaging to determine the aggressiveness of breast disease, to select a course of therapy and to assess its effectiveness sometimes after just one cycle of treatment—and to eliminate unnecessary surgeries after treatment by distinguishing active tumors from residual masses. Molecular imaging is also used to minimize the number of axillary lymph nodes removed by determining which nodes are most likely to contain cancer cells.

The molecular imaging technologies currently being used for breast cancer include:

  • positron emission tomography (PET) scanning and PET in conjunction with computer-aided tomography (CT) scanning (PET-CT)
  • molecular image-guided sentinel node biopsy
  • breast-specific gamma imaging (BSGI). 

 

What is PET?

PET involves the use of an imaging device (PET scanner) and a tiny amount of radiotracer that is injected into the patient’s bloodstream. A frequently used PET radiotracer is fluorodeoxyglucose (FDG), which the body treats like the simple sugar glucose. It usually takes between 30 and 60 minutes for the FDG distribution throughout the body to become fixed. A CT is also obtained on the same machine so the FDG and CT scans can be fused together and compared.

 

How is PET used for breast cancer?

Physicians use PET-CT studies to:

  • diagnose and stage: by determining the exact location of a tumor, the extent or stage of the disease and whether the cancer has spread in the body, especially the lymph nodes
  • plan treatment: by selecting the most effective therapy based on the unique molecular properties of the disease and of the patient, and to determine a site that is appropriate for biopsy, if necessary
  • evaluate the effectiveness of treatment: by determining the patient’s response to specific drugs and ongoing therapy. Based on changes in cellular activity observed on PET/CT images, treatment plans can be quickly altered
  • manage ongoing care: by detecting the recurrence of cancer.

 

Advantages of PET

PET helps physicians and their patients:

  • gain a clear understanding of where and how aggressive the disease is
  • select a course of treatment
  • determine the effectiveness of treatments after just one cycle of treatment
  • eliminate unnecessary surgeries after treatment by distinguishing active tumors from residual masses.

 

What is a sentinel node biopsy?

When breast cancer spreads, cancer cells are often found in the lymph nodes that are located under the arm, called axillary lymph nodes. The lymph nodes in this armpit region drain lymph from the breast and nearby areas. To determine if cancer has spread to a patient’s lymph nodes, the axillary lymph nodes are surgically resected in addition to removing part or all of the breast. In all, five to thirty nodes are surgically removed so they may be analyzed in a laboratory for evidence of cancer.

A sentinel node biopsy is an established alternative to axillary lymph node dissection. Molecular imaging is used to identify the first few, or sentinel, nodes into which a tumor drains. Sentinel nodes collect the fluid draining from the tumor and are most likely to contain cancer cells if the tumor has metastasized, or spread. In a sentinel node biopsy, only the sentinel nodes are surgically removed, which results in fewer complications and side effects for the patient, including lymphedema.

Prior to surgery to remove part of or the entire breast, a tiny amount of radioactive particles are injected in the area of the breast where the tumor is or around the nipple. Images may be taken to help the surgeon visualize the radiotracer’s pathway as it leaves the breast. The surgeon makes an incision underneath the arm and passes a hand-held probe over the area to measure levels of radioactivity. Only the lymph nodes that have absorbed the radiotracer are removed. In less than five percent of sentinel node biopsies, the sentinel node cannot be identified and a full axillary dissection is done.

Advantages of sentinel node biopsy

A sentinel lymph node biopsy is:

  • highly reliable in detecting cancerous cells
  • more accurate than the traditional axillary dissection in assessing whether breast cancer has spread to the lymph nodes. A negative sentinel lymph node indicates a greater than 95 percent chance that the remaining lymph nodes are also cancer-free
  • far fewer post-operative complications
  • performed on an outpatient basis
  • easier for the patient in terms of recuperation. Most patients resume regular activities within a few days and incisions generally heal within a few weeks.

 

What is breast-specific gamma imaging (BSGI)?

Breast-specific gamma imaging (also called molecular breast imaging) is a diagnostic procedure performed as a follow-up study to a mammogram that detected cancer or was inconclusive in its findings. BSGI is used to detect:

  • additional lesions missed by mammography and physical exam
  • cancers that are difficult to detect using mammography
  • breast cancer in women with dense breast tissue.

The procedure involves the use of a radiotracer called Technetium-99m-Sestamibi that is injected into the patient’s bloodstream and accumulates in malignant tissue. Images acquired with a special gamma camera modified for breast imaging reveal the distribution of the radiotracer, identifying abnormal areas.

Advantages of BSGI

Recent studies have shown that BSGI is able to:

  • identify cancers that are difficult for mammography to detect
  • provide information that helps physicians and patients choose the most appropriate treatment plan.

 

Research

In addition to identifying where cancer has spread in the body, PET is part of promising new research to help scientists better understand the biology underlying specific cancers and to predict how the disease will respond to specific treatments.

PET involves the use of an imaging device (PET scanner) and an imaging agent called radiotracer that is injected into the patient’s bloodstream. Combining the PET scan with computed tomography (CT) provides both anatomic and molecular information on the area of the body being studied.

Different radiotracers hone in on a specific chemical activity in the body. Most PET scanning today is performed with 18F-fluorodeoxyglucose (FDG), which accumulates in areas where there is a lot of sugar consumption, such as fast growing cancer cells.

But researchers are experimenting with new PET radiotracers, including fluorothymidine (FLT) that may indicate — early in the treatment process — when chemotherapy is working.

Chemotherapy is effective for many breast cancer patients, but not all. Other women respond to one chemotherapy drug, but not another. Currently, the results of systemic therapy can only be determined after a woman completes the therapy — and endures any treatment-related side effects. Studies have shown that tumors that take up less FLT tracer after treatment are more likely to respond to chemotherapy. Several trials are currently underway to validate early findings.

Another PET radiotracer called 16-alpha-[18F]-fluoroestradiol (FES) allows researchers to image the estrogen receptors on cells in the breast. FES PET may allow researchers to better understand why hormonal therapy is not effective in some women with estrogen-positive breast cancer (ER+) — and to predict which patients with ER+ cancer will respond to hormonal therapy.

Other radiotracers are being developed and tested for their ability to image the biologic characteristics of breast cancers, as well as tumor metabolic activity. The ability to image actual therapeutic targets, such as estrogen receptors or human epidermal growth factor receptor-2 (HER-2), will also allow researchers to test the effectiveness of new drugs.

 

On the Horizon

There are also many new and emerging molecular imaging technologies that may benefit breast cancer patients, including:

  • Combined imaging systems, known as hybrid imaging, that may improve accuracy and allow physicians to see how cancer is affecting other systems in the body
  • The use of PET imaging biomarkers, such as such as fluorothymidine (FLT) to show tumor proliferation and fluoroestrogen (FES) to detect estrogen receptors.
  • Positron emission mammography (PEM) PEM uses a PET scanner designed specifically for breast cancer detection and works much like PET: the patient is injected with a very small amount of FDG which travels through the body and is absorbed by breast tissue. The breast is imaged with detectors mounted on compression paddles similar to those used in traditional mammography.
  • PET combined with magnetic resonance (MR) imaging
  • Optical imaging using two techniques called diffuse optical tomography (DOT) and spectroscopy (DOS), researchers are able to analyze how light penetrates breast tissue, which provides information on blood cell content and oxygen levels. DOT may help differentiateearly-stage cancers from benign lesions and DOS shows promise as a biomarker for effective neoadjuvant (following surgery) chemotherapy.

 

Download the fact sheet: Molecular Imaging and Breast Cancer