Cancer cytology (Proceedings)


Cancer cytology (Proceedings)

While cytology does not give the practitioner the same amount of information as histopathology does, it can provide important information that is rapidly available, inexpensive, and minimally invasive. Cytology can provide important information that can change how subsequent treatment and diagnostics take place. For example, the surgical approach to a subcutaneous mass may be altered depending on whether the mass is a lipoma or a mast cell tumor. Similarly, additional staging tests may be indicated prior to surgery for a malignant mass (e.g. thoracic radiographs, evaluation of the regional lymph node) that would not be necessary for a benign mass. Similarly, intra-operative cytology can sometimes be utilized to make rapid decisions about treatment when necessary. Even if a cytologic diagnosis cannot be made in-house, one critical contribution the practitioner can make is to evaluate the quality of a sample prior to its submission to an outside lab. In the event that a sample is inadequate, additional samples can be obtained while the patient is still in the clinic.

Obtaining the sample

There are a number of different ways that cytologic samples can be obtained. These can include needle aspiration, impression smears, scrapings, swabs, and evaluation of cell pellets from fluids.

For needle aspiration, the author usually recommends between 20 and 25 gauge, 1-inch needles. A 22-gauge needle is sufficient for most masses. Smaller needles can be used for masses where blood contamination occurs or where it is expected (e.g. thyroid), and larger needles for masses that exfoliate poorly. Two techniques have been described for aspiration: the "bare needle" or "stab" technique and the "syringe technique". The "bare needle" technique works well for most masses, and is preferred for masses where blood contamination is encountered. For the "bare needle" technique, the mass is immobilized, the needle is introduced, and then rapidly introduced into different parts of the mass in a pecking fashion. Two situations in which the "syringe" technique may yield better results are for tumors that do not exfoliate well (dry needle) and for very small tumors, where there is not room to peck the needle into the mass.

In contrast to its utility in dermatologic disease, impression smears are rarely useful for external lesions when neoplasia is suspected, as surface contamination with bacteria, inflammatory cells and debris often obscures the underlying disease process. In the author's practice, impression smears are primary used to evaluate incisional biopsy samples after they are obtained, either to obtain preliminary information on the possible diagnosis or to confirm the adequacy of the sample.

In the author's practice, scrapings of superficial lesions or swabs of cavities (e.g. ears, nasal cavity, vaginal vault) are also rarely useful when neoplasia is expected, due to the risk of surface contamination.

Smears of cell pellets can often be a useful way to concentrate the cellular component of a fluid such as effusion or urine. The sample is centrifuged, the supernatant is poured off, and then the pellet can be rolled onto a glass slide using a cotton-tipped applicator. The author often finds this technique useful for evaluating urine samples when transitional cell carcinoma is suspected.

Preparing the sample

For aspirates or fluids, there are 2 different techniques that can be utilized for making the smear: These include the pull-apart technique (horizontal or vertical) and the blood smear technique. A combination of the 2 techniques can sometimes be used on the same slide. The goal is to create at least one area on the slides that contain a monolayer of cells of relatively high density. It is critical when preparing cytology slides that the slides not be exposed to formalin fumes. This is most important when shipping slides to an outside lab. Air-dried cytology samples and formalin containers should never be shipped together.

Hot topics on dvm360

Vet 2.0: A dvm360 Leadership Challenge - May 01, 2016

dvm360 sits down with Dr. Pol

DVM360 MAGAZINE - Apr 01, 2016

A national look at nonveterinary ownership