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Conventional Factors Do Not Explain Higher Mastectomy Rate in US Compared to UK

Conventional Factors Do Not Explain Higher Mastectomy Rate in US Compared to UK

EVANSTON, Indiana—Analysis of traditional factors that correlate with choice
of mastectomy or breast-conserving surgery failed to explain the significantly
higher mastectomy rates in the United States compared to the United Kingdom
seen in the international Arimidex (anastrozole), Tamoxifen, Alone or in
Combination (ATAC) trial. ATAC investigator Gershon Y. Locker, MD, noted the
striking difference "in the mastectomy rates between the two largest accruing
nations in ATAC-the United Kingdom with a 42% mastectomy rate and the United
States with a 51% mastectomy rate. This is a 21% increased risk of having a
mastectomy if enrolled in the United States compared to the United Kingdom."

Dr. Locker is associate professor of medicine at Northwestern University and
head of the division of hematology/oncology at Evanston Northwestern
Healthcare, in Evanston, Indiana. Noting that ATAC offered a unique opportunity
to examine breast surgery practices around the world, he reported that the
overall mastectomy rate in ATAC was 47%, a figure that was derived from 381
treatment centers in 21 countries. The percentage of women who underwent
mastectomy varied widely among the countries represented in ATAC, Dr. Locker
noted, from a low of 20% to a high of 97%. These differences may be explained
in part by sampling errors due to small sample size.

Univariate Predictive Factors

Among ATAC patients overall, univariate analysis identified the predictive
factors for mastectomy as:

  • tumor size 2 cm or larger;
  • nodal involvement (especially 4 or more nodes);
  • poorly differentiated tumor;
  • age 70 or older;
  • receiving adjuvant chemotherapy; and
  • being treated in a center that had enrolled 40 or fewer patients in the
    ATAC trial (considered a "rough correlate" of surgeon experience).

Factors predicting breast conservation were:

  • unknown nodal status;
  • estrogen-positive or progesterone-positive tumor;
  • body weight greater than 70 kilograms, and
  • being treated in a center that had enrolled more than 40 patients.

Compared to participants in the UK, more patients from the US were older,
had received chemotherapy, and were being treated at a center enrolling 40 or
fewer patients, all factors favoring mastectomy.

"But for every other factor, either there was no difference between the
United States and the United Kingdom or the difference favored doing greater
breast conservation in the United States rather than mastectomy," Dr. Locker
reported.

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