Vismodegib for Treatment of Basal Cell Carcinoma

Basal cell carcinoma (BCC) is the most common cutaneous malignancy. In the United States alone, the incidence of these tumors approaches or exceeds one million cases each year, and continues to increase. Actinic damage is the primary causal factor, and 85% of all lesions are located in cosmetically-sensitive areas such as the face, head, and neck. Although these tumors do not usually metastasize, their high prevalence and morbidity have established them as a significant public health problem. In addition a small percentage can cause significant morbidity or mortality.

Treatment goals for BCC focus on complete tumor removal and minimization of cosmetic and functional defects. Among the multiple therapeutic options available, including both excisional and ablative approaches, MMS is the most definitive treatment modality. MMS involves excision of the clinically apparent neoplastic lesion, processing and staining of horizontal frozen sections, stepwise microscopic analysis, meticulous mapping, and re-excision of residual neoplasm until tumor-free margins are obtained. Unlike all other excisional techniques, MMS allows visualization of the entire surgical margin, thus ensuring complete removal of the lesion while maximally preserving the surrounding normal skin.

Unfortunately, because many tumors show significant sub clinical extension, the resulting surgical defect after completion of MMS can be significantly larger than the presenting lesion, often necessitating complex, costly, and time-consuming repairs, and compromising the final cosmetic appearance or function. In addition, tumors in low-risk locations, which typically undergo simple excisions, nonetheless can require significant circumferential margins of normal tissue to ensure complete removal, again impacting cosmesis, function and or cost. Likewise, aggressive tumors such as sclerosing/morpheaform or recurrent BCC's can result in significant post surgical defects and associated morbidity and decreased function.

Presently, the treatment of BCC, whether by excisional or ablative means, incurs an estimated annual cost in excess of $600 million. An effective oral agent for the treatment of BCC could serve as an adjunct modality in the removal of primary or recurrent lesions and may be expected to significantly decrease cosmetic disfigurement as well as reduce treatment-associated costs. In fact, studies such as this one may ultimately show that oral treatment results in complete elimination of selected neoplastic lesions, thereby eliminating altogether the need for surgery in some lesions.

Vismodegib, (GDC-0449) is an orally delivered small molecule hedgehog pathway inhibitor. In tumor growth Hedgehog binding to PCTH1 (Patched) stops PCTH1 from inhibiting SMO (smoothened) signaling. In the absence of PCTH1 (e.g. loss of PCTH1 mutations) SMO signaling occurs constitutively, stimulating GLI1 (Glioma-Associated Oncogene-1) thus promoting tumor growth. Vismodegib inhibits SMO signaling through direct interaction with SMO thus preventing the activation of GLI1 and thus inhibiting tumor growth in Basal Cell Carcinomas. The investigators anticipate our study to demonstrate the feasibility, efficacy, and safety of Vismodegib in the oral treatment of BCC.

The safety, preliminary efficacy, and pharmacokinetics of Vismodegib was assessed in an open-label, multicenter, two-stage Phase I trial1. Patients had solid tumors refractory to therapy. An expansion cohort was included for patients with locally advanced or metastatic BCC (n=33). Patients received continuous administration of Vismodegib at 150 mg/day (n=17), 270 mg/day (n=15), or 540 mg/day (n=1) beginning on Day 1. Patients were treated until disease progression, intolerable toxicities, or withdrawal from the study. Response assessments for radiologically measurable disease, RECIST version 1.0 was used. CR or PR determined on 2 consecutive occasions ≥4 weeks apart. Locally advanced tumors assessed on Dermatological Examination. CR defined as disappearance of a palpable or visible tumor; PR defined as a reduction of >50% in tumor diameter. Results from this pilot study demonstrated that oral vismodegib could clear or reduce the tumor burden of BCCs with a CR in 2, PR in 16, SD in 11 and PD in 4 in patients followed over a 20 month period. No dose-limiting toxic events or grade 5 events were observed with a single grade 4 adverse event (asymptomatic hyponatremia) reported. The more significant and frequent adverse events were GI related with dysgeusia and muscle spasm reported.

Recently, one Phase II single-arm, non-randomized trial of single-agent vismodegib at 150 mg/day to progression or intolerance with 104 patients enrolled: (33 mBCC, 71 LA BCC) using the primary endpoint: Independent Review Facility (IRF) assessed overall response rate (ORR) and the secondary endpoints: Investigator-assessed ORR, progression-free survival (PFS), overall survival (OS), duration of response, and safety was also recently completed and it was announced that the study met its primary endpoint (ORR) and showed shrinkage of tumors in a pre-defined percentage of patients2. A preliminary safety assessment showed the most common adverse events were consistent with previous experience with vismodegib. The most common adverse events were muscle spasms, hair loss, altered taste sensation, weight loss, fatigue, nausea, decreased appetite and diarrhea. A detailed safety assessment is ongoing.

Since these are slow-growing tumors which are expected to respond favorably to treatment, and since all lesions will be surgically excised by MMS within 6 months of initial consultation, this study will not affect the current standard of care in the management of BCC.

After target tumor site is identified guided by either the plastic template or tattoo performed pre treatment the original lesion will be delineated using the template and concentric circles of two millimeters drawn around the central target area. A punch biopsy of the center of the lesion will then be performed and thereafter the lesion will be excised using standard Mohs procedures, with the excised tissue evaluated histologically to confirm the presence or absence of tumor. If there is residual tumor found histologically or there is scarring or there is significant inflammation present histologically additional layers will be performed using the 2mm concentric circles as a guide until all tumor is deemed to have been removed. The final wound size at the completion of Mohs surgery (i.e., upon reaching tumor-free tissue margins) will then be determined using the pre-treatment concentric margins, and compared to the lesion size at the initiation of treatment both for treatment and placebo areas. In addition, the histological extent of the lesion will be compared to the expected sub clinical extension as documented by Wolf and Zitelli as previously noted. Any subject who discontinued treatment prematurely should be encouraged to return to the clinic for the excision. Only subjects who have no histological evidence of BCC will be considered complete responders. Note that post excision antibiotics and analgesics administered to the subject prophylactically for infection and pain at the excision site must be recorded on the concomitant medication page of the CRF.