Table 1.

Assay characteristics for HER2 and the entire immuno-MRM-MS assay panel

	FFPE samples		Frozen samples
	HER2	All analytes	HER2	All analytes
LLOQ (fmol/mg protein)	10	183 (10–12 000)	2	111 (2–4400)
ULOQ (fmol/mg protein)	≥ 19 719	≥ 20 708 (411–395 523)	≥ 9985	≥ 10 503 (1079–198 230)
Inter-day total variability (CV%)	7.8%	9.2% (0.5%–52%)	5.9%	12.7% (4.9%–65%)
Endogenous measurement reproducibility (CV%)	7.7%	11.3% (3.1%–78%)	7.9%	12.4% (6.4%–54%)

The multiplexed immuno-MRM-MS assay consisting of 23 peptides was characterized in formalin fixed paraffin embedded (FFPE) and frozen tumor tissue lysate matrix. Lower limit of quantification (LLOQ) and upper limit of quantification (ULOQ) calculated from response curves (reported in fmol/mg protein), inter-day total variability and variability of endogenous signal measurement are reported (median and range are reported across all analytes).