DISCUSSION
KA is generally characterized by the rapid growth of dome-shaped nodules
with a central plug of keratin3. KAs have been
considered a variant of cutaneous squamous cell carcinoma (cSCC) and are
often reported as KA-type cSCC1.
The literature on purported
metastases from KAs is rare. Jacqueline et al. analysed 445 cases of KA
from 113 published articles and found that none of the cases resulted in
death or distant metastases4. KA usually invades the
surrounding tissues and does not metastasize. In the present case, two
nodules were observed arising from the bridge of the nose at 1.0 cm and
3.4 cm away from the primary focus region. This is the first report of
skip metastasis of KA on the nose.
The treatment of KA includes chemotherapy, surgery, photodynamic
therapy, and others. Surgical resection is the first-line treatment for
KA5 as most KA patients prefer it. In consideration of
the cosmetic request of the present patient, however, radiotherapy was
applied. The literature has a few reports on radiotherapy for KA, with
studies suggesting radiotherapy as a highly effective treatment for KA
with excellent cosmetic outcomes5, 6. There is no
uniform standard for the total, fractional dose, radiation dose, and
time of radiotherapy for KA. However, considering the similarity between
KA and SCC, we applied a high dose of 45.6 Gy of radiotherapy for this
tumour, which resulted in complete remission of the primary lesion.
The danger triangle of the face consists of the area from the bridge of
the nose to the corners of the mouth7. In this region,
the veins are valveless and communicate freely through the angular vein
with superior ophtalmic8. Thus, infection in this area
can spread easily without blocking the valves, especially with an
external force. In our case, the patient occasionally squeezed the
lesion both before and during the treatment. One month after the
radiotherapy was completed, two rapidly growing nodules were observed
near the original site of KA, and a biopsy confirmed the same pathology
as earlier. It is highly suspected that the external pressure applied by
the patient forced the tumour cells to gradually grow through the
valveless veins of the facial veins.
KA tends to invade the surrounding skin area, but it may present as
adjacent tissue skip metastasis under a trigger by an external force in
the valveless area of the danger triangle of the face. Nodules present
in this area should be treated with vigilance and any external force
should be forbidden.