Getting the most from the histopathology (Proceedings)
Biopsy and histopathology remains the gold standard diagnostic test for many conditions and for nearly all tumors and cancers. When performing this test, it is important to know what answers to look for, in order to obtain as much critical information as possible that may eventually impact the prognosis and the treatment planning. A good histopathology report will contain all the relevant findings observed in the submitted sample and, depending on the condition present, will describe details that may bear prognostic significance. Despite an excellent work by most anatomic pathologists, reports that do not contain all crucial or essential information are regularly encountered. The clinician's duty is then to correspond with the laboratory or pathologist directly, in order to obtain such information. Only then may the clinician discuss the findings with the owners and offer precise information that will lead to additional diagnostic tests, when deemed necessary, or prepare a specific therapeutic plan for the patient.
FIRST Step: the submitting clinician's responsibilities
It is often said that the information obtained from the histopathologic analysis will only be high-quality if all the steps preceding the sample submission were properly performed. The results of a recipe are only as good as the ingredients used in the first place.The sample(s) submitted must be appropriate in order to obtain correct information through its analysis. If an incisional biopsy, then it must be large and deep enough. It may be difficult to obtain large biopsies in certain anatomical sites or organs. Ideally, at least 2 (or 3 or 4) samples should be obtained and submitted. It is occasionally possible to tell, just by the appearance of a biopsy sample, if it will be of diagnostic quality or not. Samples that are too small (less than 1 mm) often will not be diagnostic or will show marked distortion. Similarly one may obtain inadequate results if the sample seems to contain mucus, necrotic material, or a blood clot. A sample that floats on the surface of the formalin may contain mostly fat and, unless a lipoma was biopsied, may not be diagnostic. Soft-tissue lesions should be biopsied at the periphery, in order to avoid a necrotic center, and to permit the observation of the junction between normal and diseased tissue. When biopsying a bone lesion, we typically aim at the center of the lesion, in order to avoid the peripherally located reactive bone. Remember that performing a biopsy on a tumor will lead to an increased risk of dissemination, and will not change its biologic behavior, with a few exceptions such as the occasional abdominal carcinomas that may seed in the peritoneal cavity or biopsy tract, when biopsied in a suboptimal manner (ex: transcutaneous biopsies of a bladder transitional cell carcinoma located in the trigone, etc.).
If the sample is the result of an excisional biopsy, when such a procedure applies, it is then crucial to submit the whole sample, with the surgical margins that were removed en bloc. If the sample is larger than 2 cm in diameter, transverse incisions can be performed to obtain slices of 1 cm thickness, and allow for better fixation in formalin. The incisions are performed on the side of the lesion where margin information is not needed which, for a cutaneous or subcutaneous tumor, would be the outermost surface (with skin) of the sample, and not the deep surface.
A proper sample:formalin ratio of 1:10 must be respected for good tissue fixation to occur. For very large samples, larger containers are required and should always be available for that eventuality. If the sample is simply too big for submission in its entirety, representative samples of the mass may be submitted. If this is done, samples of margins at higher risk of being incomplete should be obtained, and placed in separate and properly labeled containers. Furthermore, the portion of the original mass that is not submitted should be kept aside until the final report has been obtained. On a large sample where specific margin information is important, they should be ideally identified via inking (or sutures) for easier identification and to direct the pathologist's attention to these crucial surgical margins.
The submitted sample must be properly identified with the patient information on both the container and the cover. Filling the submission form as thoroughly as possible will ensure that correct answers are obtained. Signalment, history, and a clinical description of the lesion sampled all constitute vital information. This step is often partly neglected, especially on busy days, and often will negatively impact on the information obtained. Voluntarily omitting some information to "not influence the pathologist" in the interpretation is a mistake. All pertinent clinical information is helpful to obtain the best possible answers from the submitted sample. Information that should be on the submission form includes: age, sex, breed, appearance of the lesion, size, localization on the patient, duration and speed of growth, invasion in neighboring tissues, other pertinent clinical details, appearance on diagnostic imaging, biopsy type, clinical suspicion, response to empirical therapy, etc. Omitting pertinent clinical information on the submission form is one of the most common causes of incorrect interpretation of the sample by pathologists.