Abstract
Triple-negative breast cancers are known collectively to demonstrate a more aggressive clinical course and earlier recurrence than cancers of other histological subtypes. However, the literature on rare triple-negative breast cancers and the association of histological type with survival and risk of metastasis is sparse. To present the clinical and demographic characteristics, treatment patterns, and overall survival (OS) for histologically rare (<10% of breast cancers) triple-negative breast cancer types: medullary carcinoma, adenoid cystic carcinoma, and metaplastic breast carcinoma. This cohort study was performed in the US using data reported by the National Cancer Database between 2010 and 2016. Confirmed cases of medullary carcinoma, adenoid cystic carcinoma, and metaplastic breast cancer were analyzed. Univariable analyses and multivariable Cox regression models were performed. Data analysis was performed from April to May 2020. The primary outcome was 5-year OS. Secondary outcomes included site of metastasis, effect of immunohistochemistry, management, and 2-year mortality. A total of 8479 patients with breast cancer (mean [SD] age; 62.6 [14.3] years; 8435 women [99.48%]) were analyzed. Metaplastic carcinoma was the most commonly diagnosed histological type in this cohort, with 6867 patients (81%), followed by 1357 (16%) with adenoid cystic carcinoma and only 255 (3%) with medullary carcinoma. Medullary carcinoma presented earlier in life, at a median (interquartile range) age of 53 (45-62) years, compared with 62 (53-72) years for patients with adenoid cystic carcinoma and 63 (52-74) years for patients with metaplastic carcinoma. The proportion of tumors with triple-negative immunohistochemistry varied by histological type for medullary carcinoma (57 patients [22.4%]), adenoid cystic carcinoma (653 patients [48.1%]), and metaplastic carcinoma (3637 patients [53.0%]). Patients with adenoid cystic carcinoma were less likely to receive radiotherapy (711 patients [52.4%]) and chemotherapy (175 patients [12.9%]) compared with patients with medullary carcinoma (radiotherapy, 156 patients [61.2%]; chemotherapy, 190 patients [74.5%]) and metaplastic carcinoma (radiotherapy, 3416 patients [49.7%]; chemotherapy, 4709 patients [68.6%]). The 5-year OS rate was superior for patients with medullary (91.7%) and adenoid cystic carcinoma (88.4%) compared with patients with metaplastic carcinoma (63.1%). The 5-year mortality rate for adenoid cystic carcinoma was 8.33% vs 36.91% for metaplastic carcinoma. Nationally, over the course of 7 years, medullary carcinoma was most common and metaplastic carcinoma had the worst 5-year OS among the rare histological breast cancer subtypes analyzed. Factors associated with a poor prognosis for metaplastic carcinoma included advanced stage, lung metastasis, older age, and not receiving chemotherapy or radiation therapy. Future research focusing on rare subtypes of breast cancer is desirable and could inform the optimal management of these relatively understudied carcinomas.
Highlights
Breast cancer accounts for approximately 25% of all female cancers worldwide and 27% of cancers in developed countries,[1] it is the most common cancer in women globally and the second leading cause of cancer death among women in the US.[2]
The 5-year overall survival (OS) rate was superior for patients with medullary (91.7%) and adenoid cystic carcinoma (88.4%) compared with patients with metaplastic carcinoma (63.1%)
Factors associated with a poor prognosis for metaplastic carcinoma included advanced stage, lung metastasis, older age, and not receiving chemotherapy or radiation
Summary
Breast cancer accounts for approximately 25% of all female cancers worldwide and 27% of cancers in developed countries,[1] it is the most common cancer in women globally and the second leading cause of cancer death among women in the US.[2]. Rare breast cancers with triple-negative immunohistochemistry account for approximately 15% of all invasive breast cancers[4,5] and is defined as lacking the expression of estrogen receptor (ER), progesterone receptor (PR), and ERBB2 (formerly HER2) by the 14th St Gallen International Expert Consensus.[6] Compared with other breast cancer phenotypes, triple-negative breast cancers demonstrate an aggressive clinical course, and patients with such cancers exhibit earlier recurrence (1-3 years after diagnosis), with most deaths occurring within the first 5 years following treatment. Patients with triple-negative breast cancer who are treated with chemotherapy might exhibit worse outcomes than patients with other breast cancer subtypes.[8,9] More clinically efficacious targeted therapies for triple-negative breast cancer are still being investigated; anti–programmed death ligand–1 (PD-1)/PD-L1 agents are an emerging treatment modality for this breast cancer subtype and have demonstrated encouraging results.[10]
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