Squamous Cell Carcinoma

Squamous cell carcinoma (SCC) is the second most common form of skin cancer (BCC > SCC > Melanoma).  An estimated 700,000 cases of SCC are diagnosed each year in the US, resulting in approximately 2,500 deaths.  Like BCC, SCC is mainly caused by cumulative UV exposure; however, it is more dangerous than BCC because it can spread to the lymph nodes or other organs, and in some cases be fatal.

Whereas basal cells are only found in the epidermis, squamous cells are found in both the epidermis and mucosal membranes.  Thus, SCCs can also occur on the genitals and inside the mouth, nostrils, and eyelids.

SCCs often look like scaly red patches, open sores, elevated growths with a central depression, or warts.  They may also crust or bleed.

SCC in situ (also known as Bowen’s disease):  An early form of cancer that has yet to penetrate the basement membrane and is still confined to site of the original cancer cell.  Often appears as a thick scaly red rash.

Well differentiated SCC:  The cancer has penetrated the basement membrane and is now spreading through the dermis and adjacent tissues.  It is now able to metastasize (spread to other organs and form secondary tumors there)  These often appear as very thick, crusty lesions with tops that may fall off but invariably grow back.

Aggressive, poorly differentiated SCC:  The most dangerous type of SCC because it grows very quickly and has a greater tendency to metastasize.  They have a wide variety of appearances (soft, hard, open sores, etc.)


Actinic keratosis:  Common sunspots, the least dangerous type of SCC (more of a pre-cancer).  The surrounding skin often looks sun damaged (blotchy, freckled, and wrinkled).

Melanoma

Melanoma is less common than other skin cancers but is by far the most dangerous if not found early, causing the majority (75%) of deaths related to skin cancer.  More than 76,000 cases of melanoma are diagnosed in the US every year.  If the cancer is found in the early stages, it can usually be removed with surgery.  If the melanoma has spread, it will need to be treated with chemo- and immunotherapy, or radiation therapy.

 

Melanomas begin in the melanocytes (pigment-producing cells) and are caused by UV damage and genetic factors.  They may appear suddenly on the skin or develop from an existing mole.  Early signs of melanoma are summarized by the mnemonic “ABCDE”:

Asymmetry

Borders (irregular edges that are notched, uneven, or blurred)

Color (different shades of brown, black, or tan)

Diameter (>6mm, the size of a pencil eraser)

Evolving over time

HOW TO CUT: Fat

Fatty tissue is, without question, the arch nemesis of the Mohs tech.  There you are, cutting beautiful sections of non-fatty tissue when that spot of fat hits the blade and BOOM!  
It melts away, leaving a gaping hole in your section and a smudge of yellow mush on your blade.  

The problem is simple: Fat does not freeze well.  It takes a great deal more time and LN2/Freeze-It to reach the optimal cutting temperature.

Unfortunately, the temp at which fat hardens is often too cold for obtaining good sections of the non-fatty tissues that may also be present in the same sample.  If this is the case, you can use your A slide to get several cuts with full epidermis and then work on the fat for the B slide.

Step 1 - A sharp blade and a clean stage.

If your blade is getting dull, this is the perfect time to put in a new one.  The knife stage should also be free of any frost, OCT, streaks of tissue, and clumps of melted fat.  Use a piece of dry gauze to wipe residue up and away from the blade.  

Step 2 - The fat must be EXTRA COLD.

Once the tissue is lined up to the blade and you've cut through the safety layer, spray the yellowish unfrozen fat with short bursts of LN2 or Freeze-It until it turns white.  The picture on top shows fat that's a little on the warm side. (Not the best example, since I'd already frozen it and made slides for the doctor by this point)  On the bottom, the frozen fat appears more white.  The tissue may require several rounds of spraying with the LN2 before it's finally ready to cut, so patience is a must.  It's better to take an extra minute with this step than to attempt to cut too soon and waste tissue. 

Freeze artifact
with sub-epidermal splitting

CAUTION:  Excessive freezing of the block may cause freeze artifacts such as sub-epidermal splitting or the appearance of "bubbles" due to the expansion of water in the tissue or blood.  As mentioned above, you can always make the A slide with sections of non-fatty tissue at the regular cutting temperature and the B slide with fatty sections at the colder temperature.

Step 3 - Cut THICK and FAST.

Once the fat is frozen white (and STAYS white for a few seconds) discard the first one or two wafers. Double ratchet so that your sections are ~6-8µm thick and then slowly cut through the OCT until you've cut into the edge of the specimen.  Make sure that the tissue won't roll up, then grab the edge under your brush and coordinate the speed of your right hand with the guiding motion of the brush in your left.  Do not press the brush and tissue against the stage or it will stick and you won't be able to cut anything until you clean it.  If you manage to crank the wheel in a clean, swift jerk, you'll be able to get reasonable sections of some fairly fatty tissues. 

Some rolling on the bottom edge. Oops.