Early Detection of Lung Cancer with Meso Tetra (4-Carboxyphenyl) Porphyrin-Labeled Sputum

Abstract

Introduction: Early detection of lung cancer in high-risk individuals reduces mortality. Low-dose spiral computed tomography (LDCT) is the current standard but suffers from an exceedingly high false-positive rate (>96%) leading to unnecessary and potentially dangerous procedures. We, therefore, set out to develop a simple, noninvasive, and quantitative assay to detect lung cancer.

Methods: This proof-of-concept study evaluated the sensitivity/specificity of the CyPath Early Lung Cancer Detection Assay to correctly classify LDCT-confirmed cohorts of high-risk control (n = 102) and cancer (n = 26) subjects. Fluorescence intensity parameters of red fluorescent cells (RFCs) from tetra (4-carboxyphenyl) porphyrin (TCPP)-labeled lung sputum samples and subjects' baseline characteristics were assessed for their predictive power by multivariable logistic regression. A receiver operating characteristic curve was constructed to evaluate the sensitivity/specificity of the CyPath assay.

Results: RFCs were detectable in cancer subjects more often than in high-risk ones (p = 0.015), and their characteristics differed between cohorts. Two independent predictors of cancer were the mean of RFC average fluorescence intensity/area per subject (p < 0.001) and years smoked (p = 0.003). The CyPath-based classifier had an overall accuracy of 81% in the test population; false-positive rate of 40% and negative predictive value of 83%.

Conclusions: The tetra (4-carboxyphenyl) porphyrin -based CyPath assay correctly classified study participants into cancer or high-risk cohorts with considerable accuracy. Optimizing sputum collection, sample reading, and refining the classifier should improve sensitivity and specificity. The CyPath assay thus has the potential to complement LDCT screening or serve as a stand-alone approach for early lung cancer detection.

FIGURE 1

Subject enrollment and participation.

FIGURE 2

Characteristics of CyPath-stained cells. A, The intense red color of red fluorescent cells (RFCs) indicates uptake of tetra (4-carboxyphenyl) porphyrin (TCPP) and demonstrates a characteristic fluorescence when viewed after exposure to blue light (of a mercury vapor light source) through an Olympus U-MWIB3 filter. This is in contrast to surrounding background cells (A, background) which do not take up TCPP and appear dull when viewed under these conditions. B, Spectral emission profiles for the cells identified by arrowheads in A. C, Average fluorescence intensity (FI) versus log₁₀ area of cells chosen at random (green, grey, blue) and of RFCs from high-risk (orange) and cancer (black) cohorts. The distinction between large and small was based on the k-means (k = 2) partitioning of the log₁₀ area of background cells.

FIGURE 3

Receiver operating characteristic curve for the CyPath assay classifier. The accuracy of classifying each participant as cancer/no cancer was tabulated as the probability cutoff for the predictive model was varied. The red curve shows the changes in specificity and sensitivity for the CyPath assay at the different probability thresholds. The black line indicates the expected result if subjects were assigned randomly.