Selection for Herceptin by FISH Improves Survival

SAN ANTONIO—A retrospective study presented at the 24th Annual San Antonio Breast Cancer Symposium (abstract 18) has shown that breast cancer patients selected for treatment with trastuzumab (Herceptin) combination therapy on the basis of HER-2 gene amplification by fluorescent in situ hybridization (FISH) may have improved clinical benefits.

It has been nearly 15 years since Slamon and his colleagues described the characteristic molecular alteration that leads to overamplification of HER-2. This work led to the pivotal trial of trastuzu-mab plus chemotherapy vs chemotherapy alone as first-line treatment of metastatic breast cancer, which demonstrated an improved response rate with trastuzumab: 50% vs 32%, respectively.

To qualify for enrollment, patients had to overexpress HER-2 at the 2+ or 3+ level. The investigators used a standardized, semiquantitative immunohistochemistry (IHC) assay to screen for enrollment. A previous analysis demonstrated HER-2 amplification in 89% of 3+ tumors and in 24% of 2+ tumors.

Accuracy Issues

"Since trastuzumab was approved some 3 years ago to treat advanced breast cancer, we have come to realize that IHC as a detection method has some significant accuracy issues. These issues led us to evaluate a more precise and accurate way to measure overexpression," Dr. Mass said.

He explained that FISH technology has a built-in control mechanism that prevents some of the false-negatives that occur with use of IHC.

"To establish the accuracy of FISH, we retrospectively evaluated the pathology data that were established from the trastuzumab trials," Dr. Mass said.

Histologic material for FISH testing was available from 458 of 469 patients enrolled in the pivotal trial of trastuzumab combination therapy. The material consisted of archived, unstained tissue sections (44%) or previously immunostained tissue sections (56%).

"When we looked at the baseline characteristics of the two randomized groups, they were quite similar with two exceptions," he noted. "The amplified patients were much more likely to overexpress at the 3+ level, and, to some extent, they were much less likely to be estrogen-receptor positive. The rest of the baseline demographics and prognostic characteristics were similar in the two groups."

Results With FISH

FISH results using the PathVysion test were obtained in 451 patients, and HER-2 amplification was detected in 76% of the study population. The addition of trastuzumab to chemotherapy in the FISH-positive subgroup significantly improved the response rate (54% vs 30.8%, P < .0001). No such improvement was seen in the FISH-negative subgroup (38% vs 37.5%).

The addition of trastuzumab in the FISH-positive group also provided a significant survival benefit (OR, 0.71, P = .009) that was not detected in the FISH-negative group.

"You can see by the response rates in the amplified patients that there was a very large improvement in overall response rate from 31% to 54%. However, for the 106 patients who lacked gene amplification, there appears to be no gain from the addition of trastuzumab," Dr. Mass concluded.

Thus, he said, "patient selection based on HER-2 amplification by FISH may provide improved clinical benefit from trastuzumab, compared with selection by IHC. This can also confer a substantial survival benefit."

Addition of Trastuzumab to Chemotherapy Produces 50% Increase in Survival in Patients Selected by FISH

Results from three retrospective studies demonstrated that fluorescence in situ hybridization (FISH) testing of tumor tissue for HER2 gene amplification is an effective method of selecting women with HER2-positive metastatic breast cancer who will most likely respond to trastuzumab (Herceptin) therapy. Data from these studies were presented at the 37th annual meeting of the American Society of Clinical Oncology (ASCO).

In the retrospective analysis of tumor tissue from women in the phase III pivotal combination trial, those who were positive for HER2 gene amplification by FISH testing survived 50% longer—27 vs 18 months—when treated with trastuzumab plus chemotherapy, as compared to those who received chemotherapy alone.This result contrasts with the 24% increase in survival seen when the same tumors tested positive for HER2 protein overexpression by immunohistochemistry testing.

The goal of the trial was to determine how HER2 gene amplification, measured by FISH, compared with HER2 protein overexpression measured by immunohistochemistry in identifying patients for trastuzumab therapy. HER2 levels of 2+ and 3+ measured by immunohistochemistry were required for enrollment. (Overexpression is determined on a scale of 0 to 3+.)

Using the PathVysion FISH assay system, HER2 gene amplification was detected in 76% of the study population. Among those who tested positive by FISH, 89% were 3+ by immunohistochemistry and 31% were 2+. In the subgroup of FISH-positive patients, the addition of trastuzumab to chemotherapy resulted in an increase in the response rate to 54%, compared to 31% for those receiving chemotherapy alone. No improvement in response rates was seen in women whose tumors were negative for HER2 gene amplification by FISH (38% for trastuzumab with chemotherapy vs 37.5% for chemotherapy alone).

"These extensive retrospective analyses show us that measuring gene amplification with FISH testing may provide more accurate information about potential tumor response rates and improvement in survival with Herceptin," said Dr. Mass.

FISH-Positive Patients Survive Longer

Two additional retrospective FISH analyses were presented by Charles Vogel, MD, lead investigator from the University of Miami Cancer Center, and colleagues. In an analysis of a study in which trastuzumab was administered as a single agent to newly diagnosed HER2-positive metastatic breast cancer patients, 82 of 111 participants found to be positive by immunohistochemistry were also positive by FISH testing. The response rate for the subgroup found to be positive by FISH was 34%, compared with 7% for the group deemed negative by FISH and 26% for those positive by immunohistochemistry. Time to disease progression was 4.9 months for the FISH-positive group, 1.7 months for the FISH-negative group, and 3.5 months for those who were positive by immunohistochemistry testing.

In an analysis of the single-agent pivotal trial of trastuzumab as second- or third-line therapy after disease progression and one or two chemotherapy regimens, 173 of 209 patients testing positive by immunohistochemistry also tested positive by FISH. Response rates were 19% in the FISH-positive group, 0% in the FISH-negative group, and 15% in the group testing positive by immunohistochemistry. Time to disease progression was 3.2 months in the FISH-positive group, 1.9 months for FISH-negative patients, and 3.1 months for the immunohistochemistry-positive group.

Women in the FISH-positive group lived a median of 14.2 months, compared with 8.8 months for women in the FISH-negative group—an increase of 5.4 months or 61%. Overall survival for women in the trial who tested positive by immunohistochemistry was 12.8 months.