Doubling time of thymic epithelial tumours on CT: correlation with histological subtype

We retrospectively evaluated the doubling time (DT) of thymic epithelial tumours (TET) according to the histological subtype on CT.

From January 2005 to June 2016, we enrolled 53 patients who had pathologically confirmed TET and at least two CT scans. Tumour size was measured using a two-dimensional method, and the DT was calculated. DTs were compared among histological subtypes, and factors associated with rapid tumour growth (DT <180 days) were assessed.

In 42 of the 53 patients (79.2%) the tumours showed interval growth (>2 mm) during follow-up. The median DT for all tumours was 400 days (range 48-1,964 days). There were no significant differences in DT in relation to histological subtype (p = 0.177). When TETs were recategorized into three groups, i.e. low-risk thymomas (types A, AB, B1), high-risk thymomas (types B2, B3), and thymic carcinoma, DT was significantly different among the groups (median DT 436, 381 and 189 days, respectively; p = 0.031). Histological subtype (type B3 and thymic carcinoma) was the single independent predictor of rapid tumour growth.

The majority of TETs grew during follow-up with variable and relatively slow growth rates. Histological features of aggressive behaviour significantly correlated with a decreased DT and rapid growth.

• The majority of thymic epithelial tumours grew during follow-up (79.2%, 42/53). • Doubling times of thymic epithelial tumours were highly variable (median 400 days). • Histological features of aggressive behaviour significantly correlated with a decreased doubling time.