Surgical Oncology
Eliminating Positive Surgical Margins
Achieving negative surgical margins is one of the fundamental principles of surgical oncology. It can prove challenging in many oncologic surgeries, including breast conserving partial mastectomies, resections for head and neck cancer, rectal cancer, genitourinary cancer, and malignant intracranial tumors. It is critically important to achieve a final pathology specimen with a rim of normal tissue around the tumor. This assures the oncologic care team that all resectable disease has been taken out, and no malignant tissue is left behind. In multiple clinical trials, surgical margins have proven to be strongly associated with a patient’s disease-free survival and overall survival. The consequences of not achieving adequate surgical margins include poorer patient outcomes, follow up operations and re-excisions to achieve negative margins, and the need for potentially unnecessary additional treatments such as adjuvant chemotherapy and/or radiotherapy.
To address this, contemporary surgical oncologists have relied heavily on clinical judgment and histopathologic identification of margins to guide them. Increasing use of intraoperative frozen pathology also aids in decreasing the rate of positive margins. Although intraoperative frozen pathology has proven to be a powerful tool that decreases margin positive rates and reoperation rates, the accuracy of the frozen tissue section analysis compared to final pathologic analysis can be variable. Furthermore, it takes about one hour to perform one frozen pathologic assessment of margins, which significantly prolongs the operating time and consequently time and cost of the operation, as well as increased anesthesia risks for the patients. In certain oncologic surgeries where multiple frozen pathology analysis is required, this adds a significant burden to the healthcare system and increases the complication rate for patients.
Attempts to improve this intraoperative margins analysis have mainly focused on better surgical techniques, reliance on neoadjuvant chemotherapy or radiotherapy, or emerging fluorescence-based tumor margin analysis technology. These approaches do not come yet close to the gold standard of microscopy-based histopathologic analysis. Thus the best proactive step to mitigate margin positive rates is still intraoperative frozen pathology, despite its drawbacks.
There is a need for a new technique to provide rapid, repeatable, real-time, non-contact microscopy level imaging to be attained for pathologic analysis intra-operatively. Because of the non-contact approach, and high level of resolution achievable, our currently discovered technology can be a great solution for imaging the margins of a surgical cavity to check for any malignant cells reaching the margins. Unlike any other histopathologic tool, this analysis can be done with the tissue in question still in situ, and pathologic analysis can be done in a matter of seconds in real-time rather than taking up to an hour with the current standard of frozen pathology. The result would be: dramatically shortened operation times, increased throughput of surgeries per day per operating room, superior oncologic outcomes similar to frozen pathology, and decreased anesthetic complications for the patient. These significant advantages make sense from a patient care and cancer care point of view as well as from a health economics of point of view, which will encourage greater use of intraoperative pathologic analysis for everyone’s benefit.
Maximal Safe Resection
While complete resection determined by surgical margin analysis is the standard of care for most cancers, brain tumors present a more complex challenge. Unlike other cancers, many common brain tumors, such as glioma, present a diffusely infiltrative boundary. In these cases, clear surgical margins cannot be achieved safely, instead the goal of surgery is maximal safe resection (MSR). MSR is characterized by removal of the maximal extent of tumor without causing significant neurologic damage to the patient. The current standard for guiding resection surgeries is intraoperative magnetic resonance imaging (MRI) in conjunction with intraoperative pathology. While MRI provides spatial information and identifies dense tumor regions, intraoperative pathology is used to identifying microscopic tissue properties, differentiating gliosis vs. healthy tissue, white vs. gray matter and necrotic vs. living tissues. Currently, as with surgical margin analysis, frozen sectioning is the main intraoperative histopathological technique. However, frozen histology can only be performed on a macroscopically representative subset of samples and is prone to processing artifacts. Consequently, there remains a need for an in-situ histopathological imaging technique to aid in safely and maximally resecting brain tumors.
Currently, work is being performed to develop a PARS® system for intraoperative guidance of brain tumor resection surgeries. Recent works using multiwavelength H&E PARS® in human brain tissues have shown comparable quality to the current gold standard for brain tumor histopathological assessment. Notably, a real-time capable PARS® microscope was applied to rapidly assess tissues enabling differentiation of gliosis from healthy tissue, necrotic from living tissues and white from gray matter in unstained human brain tissue samples. Moving forwards, this method will soon be applied to unprocessed freshly resected human brain tissue samples. Ultimately, the goal of this project is development of a real-time in-situ surgical microscopy system for intraoperative histopathological assessment of the neurosurgical operative field.
Achieving negative surgical margins is one of the fundamental principles of surgical oncology. It can prove challenging in many oncologic surgeries, including breast conserving partial mastectomies, resections for head and neck cancer, rectal cancer, genitourinary cancer, and malignant intracranial tumors. It is critically important to achieve a final pathology specimen with a rim of normal tissue around the tumor. This assures the oncologic care team that all resectable disease has been taken out, and no malignant tissue is left behind. In multiple clinical trials, surgical margins have proven to be strongly associated with a patient’s disease-free survival and overall survival. The consequences of not achieving adequate surgical margins include poorer patient outcomes, follow up operations and re-excisions to achieve negative margins, and the need for potentially unnecessary additional treatments such as adjuvant chemotherapy and/or radiotherapy.
To address this, contemporary surgical oncologists have relied heavily on clinical judgment and histopathologic identification of margins to guide them. Increasing use of intraoperative frozen pathology also aids in decreasing the rate of positive margins. Although intraoperative frozen pathology has proven to be a powerful tool that decreases margin positive rates and reoperation rates, the accuracy of the frozen tissue section analysis compared to final pathologic analysis can be variable. Furthermore, it takes about one hour to perform one frozen pathologic assessment of margins, which significantly prolongs the operating time and consequently time and cost of the operation, as well as increased anesthesia risks for the patients. In certain oncologic surgeries where multiple frozen pathology analysis is required, this adds a significant burden to the healthcare system and increases the complication rate for patients.
Attempts to improve this intraoperative margins analysis have mainly focused on better surgical techniques, reliance on neoadjuvant chemotherapy or radiotherapy, or emerging fluorescence-based tumor margin analysis technology. These approaches do not come yet close to the gold standard of microscopy-based histopathologic analysis. Thus the best proactive step to mitigate margin positive rates is still intraoperative frozen pathology, despite its drawbacks.
There is a need for a new technique to provide rapid, repeatable, real-time, non-contact microscopy level imaging to be attained for pathologic analysis intra-operatively. Because of the non-contact approach, and high level of resolution achievable, our currently discovered technology can be a great solution for imaging the margins of a surgical cavity to check for any malignant cells reaching the margins. Unlike any other histopathologic tool, this analysis can be done with the tissue in question still in situ, and pathologic analysis can be done in a matter of seconds in real-time rather than taking up to an hour with the current standard of frozen pathology. The result would be: dramatically shortened operation times, increased throughput of surgeries per day per operating room, superior oncologic outcomes similar to frozen pathology, and decreased anesthetic complications for the patient. These significant advantages make sense from a patient care and cancer care point of view as well as from a health economics of point of view, which will encourage greater use of intraoperative pathologic analysis for everyone’s benefit.
Maximal Safe Resection
While complete resection determined by surgical margin analysis is the standard of care for most cancers, brain tumors present a more complex challenge. Unlike other cancers, many common brain tumors, such as glioma, present a diffusely infiltrative boundary. In these cases, clear surgical margins cannot be achieved safely, instead the goal of surgery is maximal safe resection (MSR). MSR is characterized by removal of the maximal extent of tumor without causing significant neurologic damage to the patient. The current standard for guiding resection surgeries is intraoperative magnetic resonance imaging (MRI) in conjunction with intraoperative pathology. While MRI provides spatial information and identifies dense tumor regions, intraoperative pathology is used to identifying microscopic tissue properties, differentiating gliosis vs. healthy tissue, white vs. gray matter and necrotic vs. living tissues. Currently, as with surgical margin analysis, frozen sectioning is the main intraoperative histopathological technique. However, frozen histology can only be performed on a macroscopically representative subset of samples and is prone to processing artifacts. Consequently, there remains a need for an in-situ histopathological imaging technique to aid in safely and maximally resecting brain tumors.
Currently, work is being performed to develop a PARS® system for intraoperative guidance of brain tumor resection surgeries. Recent works using multiwavelength H&E PARS® in human brain tissues have shown comparable quality to the current gold standard for brain tumor histopathological assessment. Notably, a real-time capable PARS® microscope was applied to rapidly assess tissues enabling differentiation of gliosis from healthy tissue, necrotic from living tissues and white from gray matter in unstained human brain tissue samples. Moving forwards, this method will soon be applied to unprocessed freshly resected human brain tissue samples. Ultimately, the goal of this project is development of a real-time in-situ surgical microscopy system for intraoperative histopathological assessment of the neurosurgical operative field.
PARS® H&E images of unstained tissue in comparison to their standard histopathological preparations. The left column of images outlined in purple was taken with a brightfield microscope from an H&E stained slide requiring multiple steps of processing and staining (example shown at top of column). The right column outlined in orange, was taken with the PARS® system from unstained tissue (example shown at the top of column) therefore eliminating the need for sample processing. (a) A conventional bright field H&E image of glioblastoma with solid tumor and microvascular proliferations (red outlines). (b) A rapid acquisition PARS® image of the adjacent unstained brain tissue sample, with the region of solid tumoral tissue, and microvascular proliferations (red outlines), as in (a). (c) A standard bright field histopathological H&E image of a glioblastoma sample with a largely necrotic region (blue lines and stars), a thrombotic vessel (purple outline), and a region of solid tumor with microvascular proliferations (red outline). (d) A PARS® image acquired in a rapid acquisition mode of the same section of glioblastoma tissue, with the largely necrotic region (blue line and stars) and thrombotic vessel (purple outline), and the solid tumor region with microvascular proliferations (red outline), as in (c). A close-up of tumor cells and microvascular proliferations at the boundary between these regions is shown enclosed in the green boxes. (e) A standard bright field histopathological H&E image of a brain tissue sample with infiltrating tumor cells, adjacent to solid tumor shown in (a)–(d). (f) A PARS® multiwavelength simulated H&E image of the same section of brain tissue. [Sci Rep 10, 17211 (2020). https://doi.org/10.1038/s41598-020-74160-3].
Standard brightfield histology, compared to PARS® H&E. (a, c) Small field of view standard H&E processed white matter tissue with gliosis; perivascular oligodendrocytes are indicated by the black arrows. (b, d) High fidelity PARS® emulated H&E images of adjacent tissue sections showing the same clusters of perivascular oligodendrocytes, marked with black arrows. [Sci Rep 10, 17211 (2020). https://doi.org/10.1038/s41598-020-74160-3].
a) PARS® image of 7 μm carbon fibers. b) PARS® image of an unstained slide-mounted breast tissue sample. Scale bars for a) and b) are 50 μm. ( SREP-19-21757 DOI 10.1038/s41598-019-49849-9)
a) A large field-of-view scan of a tonsil tissue specimen using PARS® microscopy. Scale bar 1 mm. b) A high resolution zoomed-in scan of the skin margin its superficial hypercellular stratified squamous epithelium (yellow outline) and the sharp delineation with the underneath hypocellular stroma (green outline) using PARS® microscopy. Scale bar 100 μm. c) an H&E prepared tissue slice of the adjacent section of tonsil tissue. ( SREP-19-21757 DOI 10.1038/s41598-019-49849-9)a) A large field-of-view scan of a tonsil tissue specimen using PARS® microscopy. Scale bar 1 mm. b) A high resolution zoomed-in scan of the skin margin its superficial hypercellular stratified squamous epithelium (yellow outline) and the sharp delineation with the underneath hypocellular stroma (green outline) using PARS® microscopy. Scale bar 100 μm. c) an H&E prepared tissue slice of the adjacent section of tonsil tissue. ( SREP-19-21757 DOI 10.1038/s41598-019-49849-9)