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Definition

Regrowth of the tumor at the site that was treated with cryosurgery

Risk factors

 Large tumors

 Tumors with ill‐delineated margins

 Size of initial tumor (squamous cell carcinoma)

Figure 11.5 Very extensive slough of skin after cryosurgery of an equine sarcoid at the level of the chest. The largest portion of the cryonecrotic eschar has already been excised and the formation of granulation tissue has started. At this location, this is only a minor complication due to the absence of important underlying structures. The wound will heal by second intention.

Source: Ann Martens.

Pathogenesis

Tumor recurrence occurs when the lesion has not been entirely and/or sufficiently frozen.

To ensure destruction of all tumoral cells, the obtained tissue temperature should be low enough over the entire volume of tumoral tissue (see Intraoperative Complication: Correct Cryosurgical Technique above).

Clinically, it has been shown that the risk of recurrence of limbal squamous cell carcinomas after cryosurgery is significantly influenced by the size of the initial tumor [5]. However, in another study, no significant correlation between recurrence and tumor or patient characteristics was found [4].

Diagnosis and monitoring

Tumor regrowth usually takes several weeks to develop and initially it may be difficult to differentiate new tumoral tissue from young irregular granulation tissue in the cryosurgical wound healing by second intention. The definitive diagnosis of tumor recurrence is made by histopathological analysis of a tissue sample. For equine sarcoids treated by cryosurgery, diagnosis of recurrence is facilitated by BPV‐DNA analysis of a superficial swab of the suspected tissue [26].

Prevention

 Correct choice of cryogen and cryosurgical equipment to allow sufficient fast and deep freezing of the tumoral tissue (see above).

 Correct cryosurgical technique including the use of a thermocouple needle to monitor tissue temperature in and around the lesion (see above). To ensure freezing of the entire tumor, an appropriate margin of visibly normal tissue should be included. In more than 70% of equine sarcoids, the surrounding normal skin still contains BPV‐DNA at 8 mm from the tumor border [27], making it advisable to include at least that margin in the freezing process. For ocular squamous cell carcinomas, a 2‐ to 3‐mm margin has been advised [5].

Treatment

The cryosurgical procedure can be repeated taking into account the above‐mentioned preventive measures. Several other tumor treatment modalities can be applied, such as (laser) excision, chemotherapy, topical treatments, and BCG vaccination.

Expected outcome

For equine sarcoids it should be kept in mind that recurrent tumors have been reported to have a lower response rate to further treatment modalities [4, 28], although this has not been confirmed in another study [7].