Tumour-infiltrating lymphocytes (TILs) reflect antitumour immunity. Their evaluation
of histopathology specimens is influenced by several factors and is subject to issues
of reproducibility. ONEST (Observers Needed to Evaluate Subjective Tests) helps in
determining the number of observers that would be sufficient for the reliable estimation
of inter-observer agreement of TIL categorisation. This has not been explored previously
in relation to TILs. ONEST analyses, using an open-source software developed by the
first author, were performed on TIL quantification in breast cancers taken from two
previous studies. These were one reproducibility study involving 49 breast cancers,
23 in the first circulation and 14 pathologists in the second circulation, and one
study involving 100 cases and 9 pathologists. In addition to the estimates of the
number of observers required, other factors influencing the results of ONEST were
examined. The analyses reveal that between six and nine observers (range 2–11) are
most commonly needed to give a robust estimate of reproducibility. In addition, the
number and experience of observers, the distribution of values around or away from
the extremes, and outliers in the classification also influence the results. Due to
the simplicity and the potentially relevant information it may give, we propose ONEST
to be a part of new reproducibility analyses.
