ESTRO 2024 - Abstract Book

S675

Clinical - Breast

ESTRO 2024

Results:

Of the 4,004 patients included, 625 (16%) did not receive any postoperative systemic therapy, 1,185 (30%) received endocrine only, 994 (25%) chemotherapy only, and 1,200 (30%) chemotherapy and endocrine therapy, without differences between the randomisation arms.

Administration and type of therapy was associated with age, menopausal status, clinical T- and N-stage and ER status (p<0.0001) (Table 1).

Patients who received systemic therapy, mainly chemotherapy, were more likely to receive chest wall RT or boost after BCT. The cumulative incidence of local recurrence rates at 15 years were 7.5% for patients who received chemotherapy (HR=0.685, 95%, CI=0.441-1.064, p-value=0.092), 4.7% for endocrine therapy-only (HR=0.555, 95%, CI=0.376-0.818, p-value=0.0029) and 4.4% for both (HR=0.449, 95%, CI=0.283-0.713, p-value=0.0007), compared to 10.7% cumulative incidence rates in the group that did not receive any systemic therapy. The Fine & Gray model showed no significant interaction between type of surgery (BCT vs. mastectomy) and adjuvant systemic treatment and no significant effect of IM-MS RT on local recurrence. The observed rate of distant metastases, regional recurrences and deaths due to breast cancer was higher for those who had adjuvant chemotherapy. Table 1: Chi squared test to investigate the association between the baseline characteristics and systemic therapy.

Adjuvant systemic therapy No systemic therapy

Chemotherapy (N=994) (%)

Endocrine therapy (N=1.185) (%)

Both

p value

(N=625) (%)

(N=1.200) (%)

(Chi square test) <.0001

Age

<45 yr

95

337

54

233

(N=719)

(15.2)

(33.9)

(4.6)

(19.4)

45-<55 yr

215

412

277

485

(N=1.389) 55-<65 yr

(34.4)

(41.5)

(23.4)

(40.4)

195

181

466

362

(N=1.204)

(31.2)

(18.2)

(39.3)

(30.2)

<>=65 yr

120

64

388

120

(N=692)

(19.2)

(6.4)

(32.7)

(10.0)

Menopausal status

<.0001

Pre menopausal

252

623

206

559

(N=1.640)

(40.3)

(62.7)

(17.4)

(46.6)

Post menopausal

373

371

979

641

(N=2.364)

(59.7)

(37.3)

(82.6)

(53.4)

Pathological T stage

<.0001