Histology is an important predictor of the behavior of breast cancer. We aim to study the impact of histology on the overall survival (OS) of breast cancer patients. We studied 11,085 breast cancer patients diagnosed with T1–T2 tumors, clinically node-negative and non-metastatic, from 2004 to 2019 included in the National Cancer Database. Kaplan–Meier curves, log-rank tests and Cox regression models were used to study the impact of histology and other variables on OS. In our patient population, 8678 (78.28%) had ductal cancer (IDC), while 2407 (21.71%) had lobular cancer (ILC). ILC patients were significantly more likely to be older, Caucasian, have a lower grade at diagnosis and be hormone receptor-positive compared to IDC patients. There was no statistically significant difference in the 5-year OS of early stage ductal (16.8%) and lobular cancer patients (16.7%) (p = 0.200). Patients of Hispanic and African American origin had worse OS rates compared to non-Hispanic and Caucasian patients, respectively. For node-positive disease, HER2+ tumors and triple-negative tumors, chemotherapy had a positive influence on OS (HR 0.85, 95% CI 0.77–0.93, p = 0.0012). Histology did not have a significant impact on the 5-year OS of early stage breast cancer patients.

6091 Background: Gemcitabine is an antimetabolite agent that has demonstrated activity in various solid and hematological malignancies. Although thrombocytopenia is a known side effect, gemcitabine-related thrombocytosis has been uncommonly reported. Chemotherapy increases the risk of thrombo-embolism in patients with cancer. The study aimed to identify the incidence of gemcitabine-related thrombocytosis and to determine whether it has been associated with an increased risk of thrombo-embolism. Methods: Medical records of 175 consecutive adults patients with a malignant disease who received gemcitabine at Saskatoon Cancer Center were reviewed. Patients with history of prior thrombo-embolism or with baseline thrombocytosis were excluded. Fisher’s Exact test was done for statistical analysis. Results: 149 eligible patients with median age of 62 (26–83) and M:F of 1.01:1 were identified. 141 (95%) patients had advanced malignancy and 61 (41%) had received prior chemotherapy. 106 (71%) patients received combination of chemotherapy and 95% of those patients received gemcitabine in combination with a platinum compound. Median number of cycle was 3 (1–8). Median platelets count prior to commencement of gemcitabine was 285 × 10⁹ (44–449). 83 (56%) patients experienced thrombocytopenia whereas 69 (46%) patients experienced thrombocytosis within 3 weeks of treatment with gemcitabine. Median post-gemcitabine platelet count in patients with thrombocytosis was 622 × 10⁹ (457–1385). 15 (10%) patients experienced thrombocytosis with each cycle of gemcitabine. Median duration of thrombocytosis was 2 weeks (0.5−5). 13 (9%) of 149 patients experienced a vascular event (venous, n=9; arterial, n=4) within 6 weeks of treatment with gemcitabine. Median platelet count prior to the vascular event was 268 × 10⁹ (79–669). All except one patient had advanced malignancy and 85% had received combination of chemotherapy. 5 of 69 (7%) patients with thrombocytosis experienced a vascular event compared with 8 of 80 (10%) patients without thrombocytosis (p=0.77). Conclusions: Gemcitabine has been associated with an increased incidence of thrombocytosis. However gemcitabine-related thrombocytosis is a transient phenomenon and has not been associated with an increased risk of a vascular event. No significant financial relationships to disclose.