Presence of non-Newtonian fluid in invasive pulmonary mucinous adenocarcinomas impacts fluorescence during intraoperative molecular imaging of lung cancer

Intraoperative molecular imaging (IMI) with folate-targeted NIR tracers has been shown to improve lesion localization in more than 80% of lung adenocarcinomas. However, mucinous adenocarcinomas (MAs) and invasive mucinous adenocarcinomas (IMAs) of the lung, which are variants of adenocarcinoma, appear to have decreased fluorescence despite appropriate folate receptor expression on the tumor surface. We hypothesized that the etiology may be related to light excitation and emission through non-Newtonian fluid (mucin) produced by goblet and columnar cancer cells.

Intraoperative data for 311 subjects were retrospectively reviewed from a prospectively collected 6-year database. For standardization, all patients underwent infusion of the same targeted molecular optical contrast agent (pafolacianine, folate receptor-targeted NIR fluorochrome) for lung cancer resections. Then, the ratio of the mean fluorescence intensity of the tumors and background tissues (TBR) was calculated. Tumors were examined for mucin, FRa, FRb, and immunofluorescent tracer uptake by a board-certified pathologist. The optical properties of mucin analyzed by imaging software were used to create in vitro gel models to explore the effects on NIR tracer fluorescence intensity.

A large proportion (192, 62%) of the patients were female, with an average of 62.8 years and a 34-year mean pack smoking history. There were no severe (Clavien–Dindo > III) complications related to pafolacianine infusion. A total of 195 lesions in the study were adenocarcinomas, of which 19 (6.1%) were of the mucinous subtype. A total of 14/19 of the patients had a smoking history, and more than 74% of the IMA lesions were in the lower lobes. IMA lesions had a lower in situ TBR than nonmucinous adenocarcinomas (2.64 SD 0.23) vs (3.45 SD 0.11), respectively (p < 0.05). Only 9/19 (47%) were localized in situ. Tumor bisection and removal of mucin from IMAs significantly increased pafolacianine fluorescence, with resultant TBR not being significantly different from the control group (4.67 vs 4.89) (p = 0.19). Of the 16 lesions that underwent FR expression analysis, 15/16 had FR presence on cancer cells or tumor-associated macrophages in the tumor microenvironment. There was no statistically significant difference in fluorescence intensity during immunofluorescence analysis (4.99 vs 5.08) (p = 0.16). Physical removal of mucin from IMAs improved the TBR from 3.11 to 4.67 (p < 0.05). In vitro analysis of the impact of synthetic non-Newtonian fluid (agarose 0.5%) on NIR tracer fluorescence showed a decrease in MFI by a factor of 0.25 regardless of the concentration for each 5 mm thickness of mucin.

The mucinous subtype of lung adenocarcinomas presents a unique challenge in pafolacianine-targeted IMI-guided resections. The presence of non-Newtonian fluids presents a physical barrier that dampens the excitation of the tracer and fluorescence emission detected by the camera. Knowledge of this phenomenon can allow the surgeon to critically analyze lesion fluorescence parameters during IMI-guided lung cancer resections.