Short-term and long-term clinical outcomes of uncommon types of invasive breast cancers

Abstract

Background

Invasive ductal carcinoma (IDC) and invasive lobular carcinoma (ILC) are predominant and well-documented types of invasive breast cancers (IBC). However, clinical outcomes of other types of IBC (i.e., uncommon IBC), which collectively account for about 20% of all IBC cases, are largely unknown.

Methods

We identified all IBC cases diagnosed in 2004-2006 (n=159,293) and 2010-2011 (n=118,822) from the Surveillance, Epidemiology and End Results (SEER) database. Uncommon IBC included mixed IDC and ILC (MDLC), IDC mixed with other types of carcinoma (IDC-MO), ILC mixed with other types of carcinoma (ILC-MO), and other-type of breast cancers (OC). We estimated overall survivals (OS) and cancer-specific survivals in multivariate regression models.

Results

Compared with IDC, MDLC was associated with a better OS (adjusted hazard ratio [aHR]=0.92, P<0.001 at approximately 10-year follow-up; aHR=0.88, P=0.01 at approximately 4-year follow-up) while OC had a worse OS (aHR=1.06, P=0.005 at approximately 10-year follow-up; aHR=1.23, P<0.001 at approximately 4-year follow-up). Other uncommon IBCs had an OS similar to IDC. Heterogeneity in survivals was observed in some subtypes of OC, with better OS in MDLC and tubular carcinoma. Radiotherapy extended OS for all types of IBC in older women (50+ years). For younger women (<50 years), radiotherapy improved OS in women with IDC, but not ILC or uncommon IBC. Radiotherapy did not change cancer-specific survival of any IBC in younger women.

Conclusions

Uncommon IBCs have distinct patterns in prognosis and survival. Effectiveness of radiotherapy in women with uncommon IBC may differ by age. The underlying mechanisms warrant further studies.

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